Expansion device

ABSTRACT

To provide an expansion device that is configured compact in size and capable of effectively preventing an abnormal rise in pressure within the expansion device caused by the differential pressure across the expansion device. An expansion device according to the present invention cancels part of refrigerant pressure by a pressure-canceling structure. More specifically, by the amount of pressure received by a valve-closing pressure-receiving surface, the elastic force required of a spring can be reduced. As a result, a small-sized spring can be employed as the spring, and the entire expansion device can be made compact in construction. Further, when the differential pressure across the expansion device has become equal to or higher than a predetermined value, a relief mechanism enables refrigerant flowing in from the upstream side to escape into a passage other than a refrigerant passage through a valve element. This makes is possible to prevent an abnormal rise in the refrigerant pressure inside the expansion device, thereby preventing breakage or the like of the internal components.

CROSS-REFERENCES TO RELATED APPLICATIONS, IF ANY

This application claims priority of Japanese Application No. 2003-315493filed on Sep. 8, 2003 and entitled “EXPANSION DEVICE” and No.2004-070947 filed on Mar. 12, 2004, entitled “EXPANSION DEVICE”.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to an expansion device that is disposed ina flow passage of refrigerant circulating through a refrigeration cycle,and comprises a differential pressure valve for controlling differentialpressure thereacross.

(2) Description of the Related Art

Conventionally, a refrigeration cycle for an automotive air-conditioneris known which uses an accumulator that performs gas/liquid separationby storing excess refrigerant on an outlet side of an evaporator, and anexpansion device of a supercooling degree control type that comprises anorifice (restriction flow passage) that controls the flow rate ofrefrigerant in response to changes in the supercooling degree anddryness of high-pressure refrigerant flowing out from a condenser, and adifferential pressure valve that provides control such that apredetermined degree of supercooling of the refrigerant is obtained(e.g. Japanese Unexamined Patent Publication (Kokai) No. H11-257802).

The expansion device of this type comprises a cylinder fixed withinpiping of the refrigeration cycle, and a valve element disposed withinthe cylinder. The valve element slides within the cylinder while beingsupported by a compression spring or the like. Refrigerant passages,including a predetermined orifice, are formed at a boundary between theinside of the valve element and the cylinder such that movement of thevalve element within the cylinder in response to a change in thedifferential pressure across the expansion device causes a change in theflow passage of refrigerant. That is, so long as the differentialpressure across the expansion device is small, the flow passage ofrefrigerant is set to the predetermined orifice, and when thedifferential pressure has become equal to or higher than a predeterminedvalue, a flow passage of refrigerant is added to thereby prevent anabnormal rise in the pressure of refrigerant.

Further, from the viewpoint of preventing an abnormal rise in thepressure within the expansion device to protect the internal componentsthereof, a safety rapture plate formed by a thin plate is provided inpart of the cylinder in advance, and when the differential pressure hasbecome equal to or higher than a predetermined value, rupture of theplate is caused to relieve the pressure.

However, in the above-described configuration of the expansion device,to enable the valve element to normally operate under high-pressureconditions, it is necessary to secure the elastic force of thecompression spring or the like, and hence a large-sized compressionspring need be used. This increases the size of the entire expansiondevice, resulting in increased manufacturing costs thereof.

SUMMARY OF THE INVENTION

The present invention has been made in view of these points, and anobject thereof is to provide an expansion device that is configuredcompact in size and capable of effectively preventing an abnormal risein pressure within the expansion device caused by the differentialpressure across the expansion device.

To solve the above problems, the present invention provides an expansiondevice that is disposed in a flow passage of refrigerant circulatingthrough a refrigeration cycle, for passing the refrigerant introducedfrom an upstream side thereof through an internal refrigerant passagethereof to thereby cause decompression of the refrigerant and allow thedecompressed refrigerant to flow downstream, and is equipped with arelief mechanism that is operable when a differential pressure acrossthe expansion device has become equal to or higher than a predeterminedvalue, to open a flow passage other than the refrigerant passage whichis closed by a valve element urged by an elastic member disposed withinthe expansion device, to thereby allow at least part of the refrigerantflowing in from the upstream side to escape via the flow passage to flowdownstream, the expansion device comprising a pressure-cancellingstructure that cancels part of pressure of the refrigerant acting on thevalve element in a valve-opening direction.

Further, the present invention provides an expansion device that isdisposed in a flow passage of refrigerant circulating through arefrigeration cycle, comprising a cylinder in the form of a hollowcylinder, the cylinder having a first valve seat formed by a steppedportion provided inside the hollow cylinder, a first valve element thathas a body in the form of a hollow cylinder inserted in the cylinder,and includes a valve portion that forms part of the body and can beremovably seated on the first valve seat, a guided portion that isguided along an inner peripheral surface of the cylinder when the bodyis moved to and away from the first valve seat, and a first refrigerantpassage that extends through an inside of the body and has a steppedportion formed therein at which the first refrigerant passage isexpanded in an upstream-to-downstream direction, the first refrigerantpassage allowing passage of the refrigerant, a first elastic member thatis disposed within the cylinder, for urging the first valve element in avalve-closing direction, a pressure-cancelling structure that cancels atleast part of pressure of the refrigerant acting on the first valveelement in a valve-opening direction, the pressure-cancelling structurecomprising a valve-closing pressure-receiving surface that receivespressure of the refrigerant acting on the first valve element in thevalve-closing direction and has a pressure-receiving area smaller than apressure-receiving area of a valve-opening pressure-receiving surfacethat receives pressure of the refrigerant acting on the first valveelement in the valve-opening direction, a first relief mechanism that isoperable when a differential pressure across the expansion device hasbecome equal to or higher than a first predetermined value to cause thevalve portion to be moved away from the first valve seat, to allow atleast part of the refrigerant flowing in from an upstream side to escapeinto a flow passage other than the first refrigerant passage within thecylinder to thereby allow the refrigerant to flow downstream, an innershaft member in the form of a hollow cylinder that is formed thereinwith a flow-restricting portion having a cross-section smaller than across-section of the first refrigerant passage, and is partiallyinserted into an expanded side of the stepped portion of the first valveelement, the inner shaft member protruding downstream from the firstvalve element, an inner cylinder in the form of a hollow cylinder thatis fixed to an inside of the cylinder, and has at least one slit formedthrough a side wall of an upstream end thereof, the upstream end beingcapable of having a downstream end of the inner shaft member engagedthereat, the inner cylinder being formed with a communication holeextending therethrough for communication with the flow-restrictingportion, a second valve element that has a body in the form of a hollowcylinder inserted in the inner cylinder, the second valve elementincluding a valve portion that forms part of the body of the secondvalve element and can be removably seated on a second valve seat formedon a downstream end face of the inner shaft member, a guided portionthat is guided along the communication hole when the body of the secondvalve element is moved to and away from the second valve seat, and asecond refrigerant passage that extends through an inside of the body ofthe second valve element and has a cross-section smaller than thecross-section of the flow-restricting portion, a second elastic memberthat is disposed within the inner cylinder, for urging the second valveelement in a valve-closing direction, and a second relief mechanism thatis operable when the differential pressure across the expansion devicehas become equal to or higher than a second predetermined value smallerthan the first predetermined value to cause the valve portion of thesecond valve element to be moved away from the second valve seat, toallow at least part of the refrigerant flowing in from the upstream sideto escape into a flow passage other than the second refrigerant passagewithin the inner cylinder to thereby allow the refrigerant to flowdownstream.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description when takenin conjunction with the accompanying drawings which illustrate preferredembodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view showing an expansion device according to afirst embodiment, in a state disposed in piping of a refrigerationcycle.

FIGS. 2A and 2B are longitudinal cross-sectional views of the expansiondevice.

FIGS. 3A and 3B are transverse cross-sectional views of the expansiondevice.

FIG. 4 is an explanatory view showing the relationship between thedifferential pressure across the expansion device and the opening areaof the refrigerant passage therethrough.

FIGS. 5A, 5B and 5C are cross-sectional views of an expansion deviceaccording to a second embodiment.

FIGS. 6A, 6B and 6C are cross-sectional views of an expansion deviceaccording to a third embodiment.

FIGS. 7A, 7B and 7C are longitudinal cross-sectional views of anexpansion device according to a fourth embodiment.

FIG. 8 is a cross-sectional view taken on line E-E of FIG. 7A.

FIG. 9 is an explanatory view showing the relationship between thedifferential pressure across the expansion device and the opening areaof the refrigerant passage therethrough.

FIGS. 10A, 10B and 10C are longitudinal cross-sectional views of anexpansion device according to a fifth embodiment.

FIGS. 11A, 11B and 11C are longitudinal cross-sectional views of anexpansion device according to a sixth embodiment.

FIG. 12A to 12E are cross-sectional views of the configuration of aninner cylinder as a component element of the expansion device.

FIGS. 13A, 13B and 13C are longitudinal cross-sectional views of anexpansion device according to a seventh embodiment.

FIG. 14 is a cross-sectional view taken on line G-G of FIG. 13A.

FIGS. 15A, 15B and 15C are longitudinal cross-sectional views of anexpansion device according to an eighth embodiment.

FIG. 16 is an explanatory view showing the relationship between thedifferential pressure across the expansion device and the opening areaof the refrigerant passage therethrough.

FIGS. 17A, 17B and 17C are longitudinal cross-sectional views of anexpansion device according to a ninth embodiment.

FIG. 18 is a cross-sectional view taken on line H-H of FIG. 17A.

FIG. 19 is an explanatory view showing the relationship between thedifferential pressure across the expansion device and the opening areaof the refrigerant passage therethrough.

FIGS. 20A, 20B and 20C are longitudinal cross-sectional views of anexpansion device according to a tenth embodiment.

FIG. 21 is a cross-sectional view taken on line I-I of FIG. 20A.

FIGS. 22A, 22B and 22C are longitudinal cross-sectional views of anexpansion device according to an eleventh embodiment.

FIG. 23 is a cross-sectional view taken on line J-J of FIG. 22A.

FIG. 24 is an explanatory view showing the relationship between thedifferential pressure across the expansion device and the opening areaof the refrigerant passage therethrough.

FIGS. 25A and 25B are longitudinal cross-sectional views of an expansiondevice according to a twelfth embodiment.

FIGS. 26A and 26B are transverse cross-sectional views of an expansiondevice according to the twelfth embodiment.

FIGS. 27A, 27B and 27C are cross-sectional views of an expansion deviceaccording to a thirteenth embodiment.

FIGS. 28A, 28B and 28C are longitudinal cross-sectional views of anexpansion device according to a fourteenth embodiment.

FIG. 29 is a cross-sectional view taken on line N-N of FIG. 28A.

FIGS. 30A, 30B and 30C are longitudinal cross-sectional views of anexpansion device according to a fifteenth embodiment.

FIGS. 31A and 31B are longitudinal cross-sectional views of an expansiondevice according to a sixteenth embodiment.

FIGS. 32A and 32B are longitudinal cross-sectional views of an expansiondevice according to a seventeenth embodiment.

FIGS. 33A and 33B are transverse cross-sectional views of an expansiondevice according to the seventeenth embodiment.

FIGS. 34A, 34B and 34C are explanatory views showing the configurationof a restriction mechanism.

FIG. 35 is an explanatory view showing the relationship between thedifferential pressure across the expansion device and the opening areaof the refrigerant passage therethrough.

FIGS. 36A and 36B are longitudinal cross-sectional views of an expansiondevice according to an eighteenth embodiment.

FIGS. 37A and 37B are transverse cross-sectional views of an expansiondevice according to the eighteenth embodiment.

FIGS. 38A and 38B are longitudinal cross-sectional views of an expansiondevice according to a nineteenth embodiment.

FIGS. 39A and 39B are transverse cross-sectional views of an expansiondevice according to the nineteenth embodiment.

FIG. 40 is an explanatory view showing the relationship between thedifferential pressure across the expansion device and the opening areaof the refrigerant passage therethrough.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings.

First Embodiment

First, a first embodiment of the present invention will be described.FIG. 1 is an explanatory view showing an expansion device according tothe present embodiment disposed in piping of a refrigeration cycle.FIGS. 2A and 2B are longitudinal cross-sectional views of the expansiondevice. FIG. 3A and 3B are transverse cross-sectional views of theexpansion device, in which FIG. 3A is a cross-sectional view of theexpansion device taken on line A-A of FIG. 2A, and FIG. 3B is across-sectional view of the expansion device taken on line B-B of FIG.2A.

Referring first to FIG. 1, the expansion device 1 is disposed in thepiping 50 forming a flow passage of refrigerant circulating through arefrigeration cycle for an automotive air conditioner, and formed by adifferential pressure valve that controls a differential pressurethereacross such that a predetermined supercooling degree of therefrigerant is obtained. It should be noted that flows of refrigerantare indicated by arrows in FIG. 1 (the same applies in the following).In the following description of the configuration shown in FIG. 1, theright side and the left side, as viewed in the figure, are sometimesreferred to as the “upstream side” and the “downstream side”,respectively, with reference to the direction of flow of refrigerant.

As shown in FIG. 2A, the expansion device 1 comprises a cylinder 10 inthe form of a hollow cylinder, and a valve element 20 in the form of ahollow cylinder inserted in the cylinder 10.

The cylinder 10 has a hollow cylindrical body 11, and includes a valveseat 12 formed by a stepped portion formed at an upstream locationinside the body 11. In other words, a refrigerant passage that allowspassage of refrigerant is formed through the cylinder 10, by a smallpipe portion 13 that is formed toward the upstream end, and a large pipeportion 14 that is formed on the downstream side of the small pipeportion 13 in a manner communicating therewith such that the large pipeportion 14 has a larger passage cross-section than that of the smallpipe portion 13.

At an upstream end of the cylinder 10, a strainer 15 is fitted on aninlet of the small pipe portion 13 through which high-pressurerefrigerant is introduced, and a flange 16 is formed which extendsradially outward for securing the expansion device 1 to the piping 50.Further, the cylinder 10 has a fitting groove 10 a circumferentiallyformed in an outer periphery of the small pipe portion 13 for having anO ring fitted therein for preservation of hermeticity when the expansiondevice 1 is fixed to the piping 50. Furthermore, a stopper 17 in theform of a bottomed hollow cylinder is fixed in the cylinder 10 at alocation in the vicinity of a downstream end of the large pipe portion14, with a spring 18 interposed between the stopper 17 and the valveelement 20.

On the other hand, the valve element 20 has a stepped hollow cylindricalbody 21 inserted into the cylinder 10. The body 21 has a valve portion22 formed at an upstream end thereof such that the valve portion 22 canbe moved to and away from the valve seat 12, a guided portion 23 formedat a location downstream of the valve portion 22, for being guided alongan inner peripheral surface of the cylinder 10, and further arefrigerant passage 24 formed in a manner axially extending through thebody 21 for passage of refrigerant therethrough.

The valve portion 22 is formed to have a tapered shape such that anouter diameter thereof is progressively reduced toward the upstream endof the body 21. When the valve portion 22 is seated on the valve seat12, the foremost end of the valve portion 22 is inserted into the smallpipe portion 13 by a predetermined amount.

The guided portion 23 is formed by three protrusions 23 a extending fromthe body 21 toward the inner surface of the cylinder 10 at equalintervals (of 120 degrees), and other refrigerant passages than therefrigerant passage 24 are formed between the protrusions 23 a, to allowpassage of refrigerant. The foremost ends of the protrusions 23 a slidealong the inner surface of the cylinder 10, whereby the valve element 20can be moved to and away from the valve seat 12.

The refrigerant passage 24 has a stepped portion 25 where therefrigerant passage 24 expanded from the upstream side toward thedownstream side, and from the expanded side of the stepped portion 25,an inner shaft member 30 in the form of a hollow cylinder is insertedwhich functions as a restriction mechanism. That is, the flow passagethrough the inner shaft member 30 provides a restriction that has across-section smaller than the cross-section of the refrigerant passage24, and decompresses refrigerant flowing through the refrigerant passage24, such that the refrigerant pressure is reduced across therestriction. Although the inner shaft member 30 is supported by thevalve element 20, it is not fixed to any part of an internal structurewithin the cylinder 10, and part of the inner shaft member 30 protrudesdownward from the valve element 20, with the downstream end face thereofbeing in abutment with the bottom of the stopper 17 and held thereat,whereby the downstream movement of the inner shaft member 30 is limited.That is, although the inner shaft member 30 has the radial movement andthe axial movement thereof limited by the valve element 20 and thestopper 17, respectively, it is not fixed to any part of the internalstructure, and therefore it brings about no inconveniences such aslimiting of the movement of the valve element 20.

At a location where the stopper 17 is in contact with the inner shaftmember 30, there is formed a through hole 17 a having a larger passagecross-section than that of the passage or restriction through the innershaft member 30, thereby preventing the flow of refrigerant from beingblocked even when the inner shaft member 30 is slightly radiallydisplaced. Further, as shown in FIG. 3B, around the through hole 17 a,there are provided four slots 17 b (second through holes) that areconnected to the aforementioned other refrigerant passages than therefrigerant passage 24. The sum of flow passage areas of these fourslots 17 b is sufficiently larger than the flow passage area of a gapformed between the valve portion 22 and the valve seat 12 when the valveelement 20 is opened, which suppresses pressure loss of the refrigerantwhich can occur in the slots 17 b.

The spring 18 is formed by a compression coil spring having apredetermined elastic coefficient, and has an upstream portion thereofinserted around the body 21 of the valve element 20. The spring 18 hasone end thereof in abutment with the bottom of the stopper 17 at alocation in the vicinity of the peripheral edge thereof, and the otherend thereof in abutment with a downstream end face of the guided portion23 of the valve element 20, thereby urging the valve element 20 towardthe valve seat 12 (in the valve-closing direction) with a predeterminedelastic force thereof.

Further, the stopper 17 is equipped with an adjusting mechanism, thatis, the stopper 17 has an outer periphery formed with an externalthread, and a downstream end of the cylinder 10 is formed with aninternal thread mating with the external thread. By adjusting the amountof screwing of the stopper 17 into the cylinder 10, the position of thestopper 17 is adjusted, whereby the elastic force of the spring 18 canbe adjusted.

The expansion device 1 configured as described above is fixed to thepiping 50 as shown in FIG. 1. More specifically, the piping 50 has ajoint structure which connects between a downstream-side pipe 51 and anupstream-side pipe 52, at an location where the expansion device 1 isinstalled therein. The downstream-side pipe 51 has a stepped portion 53formed by expanding an upstream end thereof, and the downstream end ofthe upstream-side pipe 52 is inserted into the expanded portion of thedownstream-side pipe 51 whereby the two pipes are joined. Thehermeticity between these downstream-side and upstream-side pipes 51 and52 is preserved by an O ring 54 fitted in a groove formed in thedownstream end of the upstream-side pipe 52.

The expansion device 1 has its flange 16 sandwiched between the steppedportion 53 of the downstream-side pipe 51 and the downstream end face ofthe upstream-side pipe 52, whereby it is fixed within the piping 50. Thehermeticity between the expansion device 1 and the piping 50 ispreserved by the O ring 10 b provided within the fitting groove 10 a inthe cylinder 10. The expansion device 1 is not equipped with a casing orthe like for accommodating the cylinder 10, but has its cylinder 10directly fixed to the piping 50.

Next, the pressure-cancelling structure of the expansion device 1 willbe described.

As shown in FIG. 2A, in the expansion device 1, the valve portion 22 ofthe valve element 20 is formed with a valve-opening pressure-receivingsurface 26 facing upstream for receiving refrigerant pressure which actson the valve element in the valve-opening direction, as is conventionalwith the valve element. In addition, the stepped portion 25 of the valveelement 20 is formed with a valve-closing pressure-receiving surface 27for receiving refrigerant pressure which acts on the valve element 20 inthe valve-closing direction. That is, refrigerant introduced into theinner space between the stepped portion 25 of the valve element 20 andthe inner shaft member 30 applies pressure to the valve element 20 inthe valve-closing direction (rightward as viewed in FIG. 2A), to therebycancel part of the refrigerant pressure acting on the valve element 20in the valve-opening direction. In the present embodiment, the passagecross-section of the small pipe portion 13 is formed to be larger thanthe cross-section of the expanded pipe side of the stepped portion 25,so that when the valve element 20 is seated on the valve seat 12, thevalve-closing pressure-receiving surface 27 has a smallerpressure-receiving area than that of the valve-openingpressure-receiving surface 26. Therefore, the resultant of the pressurereceived at the valve-closing pressure-receiving surface 27 and theelastic force of the spring 18 acts against the refrigerant pressurereceived at the valve-opening pressure-receiving surface 26.

Next, the relief mechanism of the expansion device 1 will be described.

As shown in FIGS. 2A and 2B, in the expansion device 1, when thedifferential pressure across the expansion device 1 has become equal toor higher than a predetermined value to cause the valve portion 22 to bemoved away the valve seat 12, most of refrigerant flowing in from theupstream side is allowed to escape through the gap between the valveportion 22 and the valve seat 12, and flow downstream through theaforementioned other refrigerant passages formed between the valveelement 20 and the cylinder 10 and the slots 17 b of the stopper 17.This prevents an abnormal rise in the refrigerant pressure inside theexpansion device 1.

FIG. 4 is an explanatory view showing the relationship between thedifferential pressure across the expansion device 1 and the opening areaof the refrigerant passage(s) thereof.

As shown in FIG. 4, so long as the valve element 20 is seated on thevalve seat 12 (state shown in FIG. 2A), even if the differentialpressure rises, the opening area is held at the cross-sectional area ofthe refrigerant passage 24. Then, when the differential pressure becomeshigher than the predetermined value, the valve element 20 is moved awayfrom the valve seat 12 to allow the refrigerant to escape into the otherrefrigerant passages outside the valve element 20 to relieve therefrigerant pressure. Thus, the opening area is instantly increased(state shown in FIG. 2B).

As described above, in the expansion device 1 according to the presentembodiment, the pressure-cancelling structure cancels part of therefrigerant pressure. That is, the elastic force required of the spring18 can be reduced by the amount of pressure received at thevalve-closing pressure-receiving surface 27. As a result, a small-sizedspring can be employed for the spring 18, which enables the entireexpansion device 1 to be made compact in size.

Further, when the differential pressure across the expansion device 1has become equal to or higher than the predetermined value, therefrigerant flowing in from the upstream side can be caused to escapeinto the other refrigerant passages than the refrigerant passage 24 ofthe valve element 20, which makes it possible to prevent an abnormalrise in the refrigerant pressure inside the expansion device 1, tothereby prevent breakage or the like of the internal components.

Second Embodiment

Next, a second embodiment of the present invention will be described.FIGS. 5A to 5C are cross-sectional views of an expansion deviceaccording to the present embodiment, in which FIGS. 5A and 5B arelongitudinal cross-sectional views of the expansion device, while FIG.5C is a cross-sectional view taken on line C-C of FIG. 5A. It should benoted that components similar to those of the first embodiment will bedesignated by identical reference numerals, and description thereof isomitted.

As shown in FIG. 5A, the expansion device 201 comprises a cylinder inthe form of a hollow cylinder 210, and a valve element in the form of ahollow cylinder 220 inserted into the cylinder 210.

The cylinder 210 comprises a valve seat portion 213 as a separate memberin the form of a hollow cylinder fixed to the inside of the cylinder210, a large pipe portion 214 having a larger passage cross-section thanthat of the valve seat portion 213 and communicating with the downstreamside of the valve seat portion 213, and a guide pipe portion 215 havinga smaller passage cross-section than that of the large pipe portion 214and communicating with the downstream side of the large pipe portion214.

The valve seat portion 213 has one end opening in the upstreamdirection, and is formed with a valve seat 212 at the other end thereof,for having the valve element 220 seated thereon.

When the expansion device 201 is disposed within the piping 50, thelarge pipe portion 214 and the guide pipe portion 215 define arefrigerant passage that allows passage of refrigerant, between theseportions 214 and 215 and the piping 50.

As shown in FIG. 5C, the large pipe portion 214 has a valve portion 222,referred to hereinafter, of the valve element 220 inserted therein, anda pair of communication holes 214 a formed through upper and lowerportions of the side wall thereof, as viewed in the figure, forcommunication of the inside thereof with the above-mentioned refrigerantpassage, and defines a space portion 241 communicating with thecommunication holes 214 a, between itself and the valve element 220.

The guide pipe portion 215 has a guided portion 233, referred tohereinafter, of the valve element 220 inserted therein such that theguided portion 233 is slidably held thereby, and an orifice hole 215 a(restriction mechanism), as a restriction, formed through a centralportion of the downstream end thereof.

On the other hand, the valve element 220 has a body 221 in the form of ahollow cylinder inserted in the cylinder 201. The body 221 has the valveportion 222 formed at an upstream end thereof, for being removablyseated on the valve seat 212, and the guided portion 223 formed on thedownstream side of the valve portion 222, for being guided along theinner peripheral surface of the guide pipe portion 215. Further, arefrigerant passage 224 axially extends through the inside of the body221 to allow passage of refrigerant.

The valve portion 222 is formed to have a tapered shape such that anouter diameter thereof is progressively reduced toward the upstream endof the body 221. When the valve portion 222 is seated on the valve seat212, the foremost end of the valve portion 222 is inserted into thesmall pipe portion 213 by a predetermined amount.

The guided portion 223 is formed by a reduced-diameter portion of thebody 221, and inserted into the guide pipe portion 215. The guidedportion 223 is slid along the inner surface of the guide pipe portion215, whereby the valve element 20 can be driven forward and backwardwith respect to the valve seat 12. A spring 218 is interposed betweenthe downstream end face of the guided portion 223 and the downstream endface of the guide pipe portion 215, for urging the valve element 220toward the valve seat 212 (in the valve-closing direction) with apredetermined elastic force thereof.

The refrigerant passage 224 extends with the same cross-section from theupstream side to the downstream side, and allows passage ofhigh-pressure refrigerant flowing in via the strainer 15. Therefrigerant having passed therethrough is decompressed by passingthrough the orifice hole 215 a.

The valve seat portion 213 is equipped with an adjusting mechanism, thatis, the valve seat portion 213 has an outer periphery formed with anexternal thread, and an upstream end of the cylinder 210 is formed withan internal thread mating with the external thread. By adjusting theamount of screwing of the valve seat portion 213 into the cylinder 210,the position of the valve seat portion 213 is adjusted, whereby theelastic force of the spring 218 can be adjusted via the valve element220.

Next, the pressure-cancelling structure of the expansion device 201 willbe described.

As shown in FIG. 5A, in the expansion device 201, the valve portion 222of the valve element 220 is formed with a valve-openingpressure-receiving surface 226 facing upstream for receiving refrigerantpressure which acts on the valve element 220 in the valve-openingdirection. In addition, a downstream end face of the guided portion 223of the valve element 20 is formed with a valve-closingpressure-receiving surface 227 for receiving refrigerant pressure whichacts on the valve element 20 in the valve-closing direction. That is,refrigerant introduced into the guide pipe portion 215 via the guidedportion 223 of the valve element 220 applies pressure to the valveelement 220 in the valve-closing direction (rightward as viewed in FIG.5A), to thereby cancel part of the refrigerant pressure acting on thevalve element 220 in the valve-opening direction. In the presentembodiment, the passage cross-section of the valve seat portion 213 isformed to be larger than that of the guide pipe portion 215, so thatwhen the valve element 220 is seated on the valve seat 212, thevalve-closing pressure-receiving surface 227 has a smallerpressure-receiving area than that of the valve-openingpressure-receiving surface 226. Therefore, the resultant of the pressurereceived at the valve-closing pressure-receiving surface 227 and theelastic force of the spring 218 acts against the refrigerant pressurereceived at the valve-opening pressure-receiving surface 226.

Next, the relief mechanism of the expansion device 201 will bedescribed.

As shown in FIGS. 5A and 5B, in the expansion device 201, when thedifferential pressure across the expansion device 201 has become equalto or higher than a predetermined value to cause the valve portion 222to be moved away the valve seat 212, most of refrigerant flowing in fromthe upstream side is allowed to escape through a gap between the valveportion 222 and the valve seat 212, and introduced into the refrigerantpassage formed between the piping 50 and the cylinder 210 via the spaceportion 241 and the communication holes 214 a, to flow downstream. Thisprevents an abnormal rise in the refrigerant pressure inside theexpansion device 201 is prevented.

As described above, in the expansion device 201 according to the presentembodiment, since the pressure-cancelling structure cancels part of therefrigerant pressure, a small-sized spring can be employed for thespring 218. As a result, it is possible to make the entire expansiondevice 201 compact in size.

Further, when the differential pressure across the expansion device 201has become equal to or higher than the predetermined value, therefrigerant flowing in from the upstream side can be caused to escapeinto a flow passage other than the refrigerant passage 224 of the valveelement 220, which makes it possible to prevent an abnormal rise in therefrigerant pressure inside the expansion device 201, to thereby preventbreakage or the like of the internal components.

Third Embodiment

Next, a third embodiment of the present invention will be described.FIGS. 6A to 6C are cross-sectional views of an expansion deviceaccording to the present embodiment, in which FIGS. 6A and 6B arelongitudinal cross-sectional views of the expansion device, while FIG.6C is a cross-sectional view taken on line D-D of FIG. 6A. It should benoted that components similar to those of the first embodiment will bedesignated by identical reference numerals, and description thereof isomitted.

As shown in FIG. 6A, the expansion device 301 comprises a cylinder inthe form of a hollow cylinder 310, and a valve element 320 in the formof a hollow cylinder inserted in the cylinder 310.

The cylinder 310 includes a small pipe portion 313 slidably supporting aguided portion, referred to hereinafter, of the valve element 320, and alarge pipe portion 314 that has a larger passage cross-section than thatof the small pipe portion 313, and has a valve portion, referred tohereinafter, of the valve element 320 inserted therein. A valve seat 312is formed by a stepped portion formed on a communicating portion betweenthe small pipe portion 313 and the large pipe portion 314.

The small pipe portion 313 is, as shown in FIG. 6C, has a pair ofintroducing holes 313 a formed through upper and lower portions of theside wall, as viewed in the figure, for having refrigerant introducedtherein, with a closed upstream end of the small pipe portion 313 and adownstream end of the same communicating with the large pipe portion314. The small pipe portion 313 is expanded by a predetermined amounttoward the large pipe portion 314 to form an expanded pipe portion 313 bin the vicinity of the valve seat 312. A strainer 315 is fitted on thesmall pipe portion 313 such that it covers the small pipe portion 313from outside.

A stopper 317 in the form of a hollow cylinder is fixed to the largepipe portion 314 at a location in the vicinity of the downstream endthereof, and a spring 318 is inserted between the stopper 317 and thevalve element 320, for urging the valve element 320 in the direction ofthe valve seat 312.

On the other hand, the valve element 320 has a body 321 in the form of ahollow cylinder. The body 321 has the guided portion 322 formed at anupstream end thereof, for sliding along the inner surface of the smallpipe portion 313, and a valve portion 323 formed at a downstream endthereof, for being removably seated on the valve seat 312. Further, arefrigerant passage 324 axially extends through the inside of the body321 to allow passage of refrigerant. Further, a space portion 341communicating with the introducing holes 313 a is defined between thevalve element 320 and the small pipe portion 313, at the location of apipe portion 325 between the guided portion 322 of the valve portion 323of the valve element 320.

The pipe portion 325 has a side wall formed with an orifice hole 331that communicates between the space portion 341 and the refrigerantpassage 324, and functions a restriction mechanism, and when the valveelement 320 is seated, the refrigerant flowing in from the piping 50 isintroduced via the introducing holes 313 a and the orifice hole 331 intothe refrigerant passage 324. At the downstream end of the refrigerantpassage 324, there is formed an expanded pipe portion 332 which isexpanded by a predetermined amount for suppressing pressure loss of therefrigerant flowing through the refrigerant passage 324.

The stopper 317 is equipped with an adjusting mechanism, that is, thestopper 317 has an outer periphery formed with an external thread, and adownstream end of the cylinder 310 is formed with an internal threadmating with the external thread. By adjusting the amount of screwing ofthe stopper 317 into the cylinder 310, the position of the stopper 317is adjusted, whereby the elastic force of the spring 318 can beadjusted.

Next, the pressure-cancelling structure of the expansion device 301 willbe described.

As shown in FIG. 6A, in the expansion device 301, the valve portion 323of the valve element 320 is formed with a valve-openingpressure-receiving surface 326 facing upstream for receiving refrigerantpressure which acts on the valve element 320 in a valve-openingdirection. In addition, the downstream end of the guided portion 322 ofthe valve element 320 is formed with a valve-closing pressure-receivingsurface 327 for receiving refrigerant pressure which acts on the valveelement 320 in the valve-closing direction. That is, refrigerantintroduced into the space portion 341 through the introducing hole 313 aapplies pressure to the valve-opening pressure-receiving surface 327 ofthe valve element 320 in the valve-closing direction (rightward asviewed in FIG. 6A), and to the valve-opening pressure-receiving surface326 of the same in the valve-opening direction (leftward as viewed inFIG. 6A) to thereby cancel part of the refrigerant pressure acting onthe valve element 320 in the valve-opening direction. In the presentembodiment, since the expanded pipe portion 313 b is provided, so thatwhen the valve element 320 is seated on the valve seat 312, thevalve-closing pressure-receiving surface 327 has a smallerpressure-receiving area than that of the valve-openingpressure-receiving surface 326. Therefore, the resultant of the pressurereceived at the valve-closing pressure-receiving surface 327 and theelastic force of the spring 318 acts against the refrigerant pressurereceived at the valve-opening pressure-receiving surface 326.

Next, the relief mechanism of the expansion device 301 will bedescribed.

As shown in FIGS. 6A and 6B, in the expansion device 301, when thedifferential pressure across the expansion device 301 has become equalto or higher than a predetermined value to cause the valve portion 323to be moved away the valve seat 312, most of refrigerant flowing in fromthe upstream side is allowed to escape through a refrigerant passageformed by a gap between the valve portion 323 and the valve seat 312, toflow downstream by being guided through the large pipe portion 314. Thisprevents an abnormal rise in the refrigerant pressure inside theexpansion device 301.

As described above, in the expansion device 301 according to the presentembodiment, since the pressure-cancelling structure cancels part of therefrigerant pressure, a small-sized spring can be employed for thespring 318. As a result, it is possible to make the entire expansiondevice 301 compact in size.

Further, when the differential pressure across the expansion device 301has become equal to or higher than the predetermined value, therefrigerant flowing in from the upstream side can be caused to escapeinto a flow passage other than the refrigerant passage 324 of the valveelement 320, which makes it possible to prevent an abnormal rise in therefrigerant pressure inside the expansion device 301, to thereby preventbreakage or the like of the internal components.

Fourth Embodiment

Next, a fourth embodiment of the present invention will be described.FIG. 7A to 7C are longitudinal cross-sectional views of an expansiondevice according to the present embodiment, and FIG. 8 is across-sectional view taken on line E-E of FIG. 7A. It should be notedthat since most of the components of the expansion device according tothe present embodiment are similar to those of the first embodiment,components similar to those of the first embodiment will be designatedby identical reference numerals, and description thereof is omitted.

As shown in FIG. 7A, the expansion device 401 comprises a cylinder 10 inthe form of a hollow cylinder, and a valve element 420 in the form of ahollow cylinder inserted in the cylinder 10.

The valve element 420 has a body 421 in the form of a stepped hollowcylinder inserted in the cylinder 10, and a valve portion 422 is formedat an upstream end of the body 421, for being removably seated on thevalve seat 12, with a refrigerant passage 424 axially extending throughthe inside of the body 421 to allow passage of refrigerant.

The valve portion 422 has a tapered end the outer diameter of whichdecreases toward the upstream end of the body 421, and an extendedportion that is extended from the tapered end by a predetermined amount,and is configured to be fitted in the small pipe portion 13 by thepredetermined amount when the valve element 420 is seated. Further, asshown in FIG. 8, a slit 431 is formed through a side wall of an upstreamend of the valve portion 422, which opens toward the small pipe portion13.

Next, the pressure-cancelling structure of the expansion device 401 isdistinguished from that of the first embodiment in that a valve-openingpressure-receiving surface 426 formed on the valve portion 422 of thevalve element 420 in a manner facing upstream, for receiving refrigerantpressure acting on the valve element 420 in the valve-opening directionhas a shape slightly different from that of the valve-openingpressure-receiving surface 26 of the first embodiment, but is the samein that the resultant of the pressure received at the valve-closingpressure-receiving surface 27 and the elastic force of the spring 18acts against the refrigerant pressure received at the valve-openingpressure receiving surface 426.

Next, the relief mechanism of the expansion device 401 will bedescribed.

As shown in FIGS. 7A to 7C, in the expansion device 401, when thedifferential pressure across the expansion device 401 has become equalto or higher than a predetermined value to cause the valve portion 422to start to be moved away the valve seat 12, part of refrigerant flowingin from the upstream side is allowed to flow downstream through arefrigerant passage formed between the valve element 420 and thecylinder 10 via the slit 431.

Then, as the differential pressure further rises, the openingcommunicating between the small pipe portion 13 and the large pipeportion 14 is progressively increased due to the slit 431, and when theupstream end of the valve portion 420 is removed from the small pipeportion 13, the opening is sharply increased, whereby most of therefrigerant flowing in from the upstream side is allowed to escape intoa flow passage other than the refrigerant passage 424 in the valveelement 420, to allow the same to flow to the downstream side.

FIG. 9 is an explanatory view showing the relationship between thedifferential pressure across the expansion device 401 and the openingarea of the refrigerant passage(s) thereof.

As shown in FIG. 9, so long as the valve element 420 is seated on thevalve seat 12 (state shown in FIG. 7A), even if the differentialpressure rises, the opening area is held at the cross-sectional area ofthe restriction of the inner shaft member 30. Then, when thedifferential pressure becomes higher than a predetermined value, therefrigerant is allowed to escape through the slit 431, which allows theopening area to be gently increased in response to changes in thedifferential pressure across the expansion device (state shown in FIG.7B). Then, when the differential pressure further rises, the upstreamend of the valve element 420 is removed from the small pipe portion 13,which instantly increases the opening area in response to a change inthe differential pressure (state shown in FIG. 7C).

As described above, in the expansion device 401 according to the presentembodiment, the refrigerant flowing in from the upstream side is allowedto escape in a stepwise manner. As a result, it is possible to preventan abnormal rise in the refrigerant pressure inside the expansion device401, to thereby prevent breakage or the like of the internal components.Further, by the stepwise relief, of the refrigerant pressure, the flowcharacteristics representative of the relationship between thedifferential pressure across the expansion device 401 and the openingarea of the refrigerant passage thereof can be set differently fromthose of the first embodiment.

Fifth Embodiment

Next, a fifth embodiment of the present invention will be described. Thepresent embodiment is an application of the configuration of the fourthembodiment to the configuration of the second embodiment. FIGS. 10A to10C are longitudinal cross-sectional views of an expansion deviceaccording to the present embodiment. It should be noted that most of theconfiguration of the expansion device according to the presentembodiment is similar to that of the second embodiment, and thereforedescription thereof is omitted by designating the similar componentswith identical reference numerals.

As shown in FIG. 10A, the expansion device 501 comprises a cylinder inthe form of a hollow cylinder 210, and a valve element 520 in the formof a hollow cylinder inserted in the cylinder 210.

A valve portion 522 of the valve element 520 has a tapered end extendedupstream by a predetermined amount such that the outer diameter thereofdecreases toward the upstream end of a body 521, and is configured to befitted in the valve seat portion 213 by the predetermined amount whenthe valve element 520 is seated. Further, a slit 531 is formed through aside wall of an upstream end of the valve portion 522, which openstoward the valve seat portion 213. It should be noted that the slit 531shown in FIGS. 10A to 10C operate similarly to the slit 431 of thefourth embodiment, and therefore description thereof is omitted.

Thus, in the expansion device 501 according to the present embodiment aswell, with the provision of the slit 531, the refrigerant flowing infrom the upstream side is allowed to escape in a stepwise manner. As aresult, the flow characteristics representative of relationship betweenthe differential pressure across the expansion device 501 and theopening area of the refrigerant passage can be configured differentlyfrom those of the first embodiment.

Sixth Embodiment

Next, a sixth embodiment of the present invention will be described. Inthe present embodiment, the relief mechanism is provided in two stages.FIGS. 11A to 11C are longitudinal cross-sectional views of an expansiondevice according to the present embodiment. In FIGS. 12A to 12E, FIG.12A is a longitudinal cross-sectional view of an inner cylinder, FIG.12B a plan view of the same, FIG. 12C a cross-sectional view taken online F-F of A, FIG. 12D a left side view, and further, FIG. 12E a rightside view. It should be noted that components similar to those of thefirst embodiment will be designated by identical reference numerals, anddescription thereof is omitted.

As shown in FIG. 11A, the expansion device 601 comprises a cylinder 602in the form of a hollow cylinder formed to be axially longer than thecylinder 10 of the first embodiment, a first relief mechanism 610inserted in a upstream part of the cylinder 602, and a second reliefmechanism 620 inserted in a downstream part of the same.

It should be noted that the first relief mechanism 610 is formed by afirst valve element 20 which is removably seated on a first valve seat12 formed by a stepped portion provided inside the cylinder 602, andhence is configured similarly to the relief mechanism of the firstembodiment. Further, the first valve element 20 also has thepressure-cancelling structure as described in the first embodiment, andhence description of the relief mechanism and the pressure-cancellingstructure will be omitted.

On the other hand, the second relief mechanism 620 comprises an innercylinder 640 formed on the downstream side of the first relief mechanism610 in a manner continuous therewith, and a second valve element 650disposed within the inner cylinder 640.

The inner cylinder 640 has a body in the form of a hollow cylinder, asshown in FIGS. 12A to 12E, which has a stepped portion 641 with areduced inner diameter formed at an upstream end thereof, and isconfigured such that the upstream end of the body can hold thedownstream end of the inner shaft member 30. Further, a communicationhole 644 is formed through the stepped portion 641, which communicateswith the restriction of the inner shaft member 30.

Further, the upstream end of the inner cylinder 640 has a side wallformed with a pair of slits 642 which opens in the upstream direction,and the downstream end of the same with a slightly-increased outerdiameter has an adjusting portion 643 constituting an adjustingmechanism, referred to hereinafter. The slits 642 communicate between arefrigerant passage formed between the inner cylinder 640 and thecylinder 602 and the inside of the inner cylinder 640, to allow passageof the refrigerant flowing through the refrigerant passage to therebyallow the refrigerant to flow downstream of the second valve element 650of the inner cylinder 640.

Referring again to FIGS. 11A to 11C, the upstream end face of the innercylinder 640 has a spring 18 in contact therewith which is interposedbetween the upstream end face of the inner cylinder 640 and the firstvalve element 20. That is, the adjusting portion 643 has an outerperiphery formed with an external thread, and a downstream end of thecylinder 602 is formed with an internal thread mating with the externalthread. By adjusting the amount of screwing of the inner cylinder 640into the cylinder 602, the position of the inner cylinder 640 isadjusted, whereby the elastic force of the spring 18 can be adjusted.Further, the downstream end of the inner cylinder 640 has a stopper 617in the form of a hollow cylinder fixed thereto, and a spring 618 (secondelastic member) having a smaller elastic constant than that of thespring 18 is interposed between the stopper 617 and the second valveelement 20.

On the other hand, the second valve element 650 has a body in the formof a hollow cylinder inserted in the inner cylinder 640, and includes avalve portion 651 and a guided portion 653 forming parts of the body. Asecond refrigerant passage 654 having a smaller cross-section than thepassage cross-section of the restriction of the inner shaft member 30extends trough the inside of the body.

The guided portion 653 has an outer diameter substantially equal to aninner diameter of the communication hole 644, and an upstream end of theguided portion 653 forms the valve portion 651. Further, on thedownstream side of the guided portion 653, a flange 652 is formed whichextends radially outward, and one end of the spring 618 is in abutmentwith the flange 652. A portion of the second valve element 650 on afurther downstream side of the flange 652 has a tapered shape the outerdiameter of which decreases downstream. The second valve element 650moves to and away from the stepped portion 641 while being guided alongthe communication hole 644. The valve portion 651 is removably seated onthe downstream end face of the inner shaft member 30 as a valve seat(second valve seat).

Further, the stopper 617 is equipped with an adjusting mechanism, thatis, the stopper 617 has an outer periphery formed with an externalthread, and a downstream end of the inner cylinder 640 is formed with aninternal thread mating with the external thread. By adjusting the amountof screwing of the stopper 617 into the inner cylinder 640, the positionof inner cylinder 640 is adjusted, whereby the elastic force of thespring 618 can be adjusted.

Next, the relief mechanism of the expansion device 601 will bedescribed.

As shown in FIGS. 11A to 11C, in the expansion device 601, when thedifferential pressure across the expansion device 601 has become equalto or higher than a first predetermined value, the first reliefmechanism 610 operates, and when the differential pressure has becomeequal to or higher than a second predetermined value, the second reliefvalve 620 operates. In the present embodiment, the first predeterminedvalue is configured to be larger than the second predetermined value,and the amount of refrigerant allowed to escape by the first reliefmechanism 610 is set to be larger than the amount of refrigerant allowedto escape by the second relief mechanism 620. Further, the second reliefmechanism 620 on the downstream side is first operated to allowrefrigerant to escape at a small flow rate, and thereafter, the firstrelief mechanism 610 on the upstream side is operated to allow therefrigerant to escape at a large flow rate.

That is, when the differential pressure across the expansion device 601has become equal to or higher than the second predetermined value, asshown in FIGS. 11A and 11B, the upstream end face of the second valveelement 650 of the second relief mechanism 620 is moved away from thedownstream end face of the inner shaft member 30 to terminate thecontact state therebetween, whereby part of refrigerant flowing throughthe restriction of the inner shaft member 30 into the communication hole644 is allowed to escape through a gap between the downstream end faceof the inner shaft member 30 and the upstream end face of the secondvalve element 650. The refrigerant flows via the slit 642 and therefrigerant passage between the inner cylinder 640 and the cylinder 602(i.e. the other different passage than the second refrigerant passage654) to the downstream side of the second valve element 650 of the innercylinder 640.

Then, when the differential pressure across the expansion device 601become equal to or higher than the first predetermined value to causethe valve portion 22 of the first relief mechanism 610 to be moved awayfrom the valve seat 12, most of the refrigerant flowing in from thedownstream side is allowed to escape via the gap between the valveportion 22 and the valve seat 12, and flow downstream via therefrigerant passage formed between the first valve element 20 and thecylinder 602, the refrigerant passage between the inner cylinder 640 andthe cylinder 602, and the slit 642. This prevents an abnormal rise inthe refrigerant pressure inside the expansion device 601.

As described above, in the expansion device 601 according to the presentembodiment, the relief mechanism is provided in two stages, i.e. as thefirst relief mechanism 610 and the second relief mechanism 620, so thatby shifting the timing of the relief of the refrigerant pressure, therefrigerant pressure inside the expansion device 601 can be reduced intwo stages. Further, by differentiating the amount of relief between thetwo mechanisms, it is possible to carry out reduction control of therefrigerant pressure in various manners. Therefore, it is possible torealize delicate pressure reduction control such that the operations ofthe internal components of the expansion device 601 are not adverselyaffected, to thereby effectively prevent breakage or the like of theinternal components.

Seventh Embodiment

Next, a seventh embodiment of the present invention will be described.In the present embodiment as well, the relief mechanism is provided intwo stages. FIG. 13A to 13C are longitudinal cross-sectional views of anexpansion device according to the present embodiment. FIG. 14 is across-sectional view taken on line G-G of FIG. 13A. It should be notedthat components similar to those of the first embodiment will bedesignated by identical reference numerals, and description thereof isomitted.

As shown in FIG. 13A, the expansion device 701 comprises the hollowcylinder 702 formed to be axially longer than the cylinder 10 of thefirst embodiment, a first relief mechanism 710 inserted in a upstreampart of the inside of the cylinder 702, and a second relief mechanism720 inserted in a downstream part of the same.

It should be noted that the first relief mechanism 710 is formed by afirst valve element 20 which is removably seated on a first valve seat12 formed by a stepped portion provided inside the cylinder 702, and thesecond relief mechanism 720 is formed by a second valve element 20 whichis removably seated on a second valve seat 752 formed by a downstreamend of a stopper 750, referred to hereinafter, disposed within thecylinder 702. Both of the mechanisms are configured similarly to therelief mechanism of the first embodiment. However, the passagecross-section of the inner shaft member 730 of the second reliefmechanism 720 is smaller than that of the inner shaft member 30 of thefirst relief mechanism 710 by a predetermined amount. It should be notedthat in FIGS. 13A to 13C, the valve-opening pressure-receiving surfaceand the valve-closing pressure-receiving surface of the first valveelement 20 on the upstream side form a first valve-openingpressure-receiving surface and a first valve-closing pressure-receivingsurface, and the valve-opening pressure-receiving surface and thevalve-closing pressure-receiving surface of the second valve element 20on the downstream side form a second valve-opening pressure-receivingsurface and a second valve-closing pressure-receiving surface.

Further, the first valve element 20 and the second valve element 20 eachhave the pressure-cancelling structure described in the firstembodiment, and hence description of the mechanism and the structurewill be omitted.

Between the first relief mechanism 710 and the second relief mechanism720, the stopper 750 in the form of a bottomed hollow cylinder isinterposed. At a location where the stopper 750 is in contact with theinner shaft member 30, there is formed a through hole 751 having alarger passage cross-section than that of the inner shaft member 30,thereby preventing the flow of refrigerant from being blocked even whenthe inner shaft member 30 is slightly radially displaced. Further, asshown in FIG. 14, part of the outer periphery of the stopper 750 isformed as a cutout portion 753 which is cut out parallel to the axis,thereby forming a refrigerant passage between the cutout 753 and thecylinder 702, which communicates between the upstream side and thedownstream side of the stopper 750.

Further, the stopper 750 is equipped with an adjusting mechanism, thatis, the stopper 750 has an outer periphery formed with an externalthread, and an inner wall of the cylinder 702 is formed with an internalthread mating with the external thread. By adjusting the amount ofscrewing of the stopper 750 into the cylinder 702, the position of thestopper 750 is adjusted, whereby the elastic force of the spring 18 canbe adjusted.

Next, the relief mechanism of the expansion device 701 will bedescribed.

As shown in FIGS. 13A to 13C, in the expansion device 701, the springconstant of the spring 18 as a component of the first relief mechanism710 and the spring constant of the spring 718 as a component of thesecond relief mechanism 720 are made different from each other, suchthat when the differential pressure across the expansion device 701 hasbecome equal to or higher than a first predetermined value, the firstrelief mechanism 710 operates, and when the differential pressure hasbecome equal to or higher than a second predetermined value, the secondrelief valve 720 operates. In the present embodiment, the firstpredetermined value is configured to be larger than the secondpredetermined value. Further, the second relief mechanism 720 on thedownstream side is first operated to allow refrigerant to escape at asmall flow rate, and thereafter, the first relief mechanism 710 on theupstream side is operated to allow the refrigerant to escape at a largeflow rate.

That is, when the differential pressure across the expansion device 701has become equal to or higher than the second predetermined value, asshown in FIGS. 13A and 13B, the valve portion 22 of the second reliefmechanism 720 is moved away from the second valve seat 752, whereby partof the refrigerant flowing in from the upstream side via the inner shaftmember 30 and the stopper 750 is allowed to escape through a gap betweenthe valve portion 22 and the valve seat 752, and flow downstream via therefrigerant passage formed between the second valve element 20 and thecylinder 702.

Then, further when the differential pressure across the expansion device701 become equal to or higher than the first predetermined value tocause the valve portion 22 of the first relief mechanism 710 to be movedaway from the valve seat 12, most of the refrigerant flowing in from theupstream side is allowed to escape via the gap between the valve portion22 and the valve seat 12, and flow downstream via the refrigerantpassage formed between the first valve element 20 and the cylinder 702,the refrigerant passage between the cutout portion 753 and cylinder 702,and the refrigerant passage between the second valve element 20 and thecylinder 702. This prevents an abnormal rise in the refrigerant pressureinside the expansion device 701.

As described above, in the expansion device 701 according to the presentembodiment, the relief mechanism is provided in two stages. Therefore,similarly to the sixth embodiment, it is possible to realize delicatepressure reduction control such that the operations of the internalcomponents of the expansion device 701 are not adversely affected, tothereby effectively prevent breakage or the like of the internalcomponents.

Eighth Embodiment

Next, an eighth embodiment of the present invention will be described.FIGS. 15A to 15C are longitudinal cross-sectional views of an expansiondevice according to the present embodiment. It should be noted thatsince most of the components of the expansion device according to thepresent embodiment are similar to those of the first embodiment,components similar to those of the first embodiment will be designatedby identical reference numerals, and description thereof is omitted.

As shown in FIG. 15A, the expansion device 801 comprises a cylinder 10in the form of a hollow cylinder, and a valve element 820 in the form ofa hollow cylinder inserted in the cylinder 10.

The valve element 820 has a body 821 in the form of a stepped hollowcylinder inserted in the cylinder 10, and a valve portion 822 is formedat an upstream end of the body 821, for being removably seated on thevalve seat 12, further with a refrigerant passage 824 axially extendingthrough the body 821 to allow passage of refrigerant.

The valve element 822 is configured to have a tapered shape the outerdiameter of which decreases toward the upstream end of the body 821, andwhen the valve element 820 is seated, the upstream end thereof isinserted into the small pipe portion 13 such that a predetermined gap isformed between the upstream end and the inner wall of the small pipeportion 13.

Next, the pressure-cancelling structure of the expansion device 801 isdistinguished from that of the first embodiment in that a valve-openingpressure-receiving surface 826 formed on the valve portion 822 of thevalve element 820 in a manner facing upstream, for receiving refrigerantpressure acting on the valve element 820 in the valve-opening directionhas a shape slightly different from that of the valve-openingpressure-receiving surface 26 of the first embodiment, but is the samein that the resultant of the pressure received at the valve-closingpressure-receiving surface 27 and the elastic force of the spring 18acts against the refrigerant pressure received at the valve-openingpressure receiving surface 826.

Next, the relief mechanism of the expansion device 801 will bedescribed.

As shown in FIGS. 15A and 15C, in the expansion device 801, when thedifferential pressure across the expansion device 801 has become equalto or higher than a predetermined value to cause the valve portion 822to start to be moved away the valve seat 12, part of refrigerant flowingin from the upstream side is leaked through the gap between the valveelement 820 and the small pipe portion 13. Further, when the upstreamend of the valve element 820 is moved away from the small pipe portion13, the refrigerant is allowed to escape at a larger flow rate, wherebythe refrigerant is allowed to escape into the other flow passage thanthe refrigerant passage 824 through the valve element 820 in a stepwiseincreasing manner, to thereby allow the refrigerant to flow downstream.

FIG. 16 is an explanatory view showing the relationship between thedifferential pressure across the expansion device 801 and the openingarea of the refrigerant passage(s) thereof.

As shown in FIG. 16, so long as the valve element 820 is seated on thevalve seat 12 (state shown in FIG. 15A), even if the differentialpressure rises, the opening area is held at the cross-sectional area ofthe refrigerant passage 824. Then, when the differential pressurebecomes higher than a predetermined value, the aforementioned gapprovides an opening, which once increases the opening area (state shownin FIG. 15B). Thereafter, as the gap continues to provide a fixedopening area, the differential pressure across the expansion device 801further rises, which causes the upstream end of the valve element 820 tobe moved away from the small pipe portion 13, which instantly increasesthe opening area in response to a change in the differential pressureacross the expansion device 801 (state shown in FIG. 15C).

As described above, in the expansion device 801 according to the presentembodiment, the refrigerant flowing in from the upstream side is allowedto escape in a stepwise manner. As a result, it is possible to preventan abnormal rise in the refrigerant pressure inside the expansion device801, to thereby prevent breakage or the like of the internal components.Further, by the stepwise relief of the refrigerant pressure, the flowcharacteristics representative of the differential pressure and theopening area of the refrigerant passage by the expansion device 801 canbe set differently from those of the first embodiment.

It should be noted that such flow characteristics can be also realizedin the sixth and seventh embodiments described above.

Ninth Embodiment

Next, a ninth embodiment of the present invention will be described.FIGS. 17A to 17C are longitudinal cross-sectional views of an expansiondevice according to the present embodiment, and FIG. 18 is across-sectional view taken on line H-H of FIG. 17A. It should be notedthat since most of the components of the expansion device according tothe present embodiment are similar to those of the first embodiment,components similar to those of the first embodiment will be designatedby identical reference numerals, and description thereof is omitted.

As shown in FIG. 17A, the expansion device 901 comprises a cylinder 10in the form of a hollow cylinder, and a valve element 920 in the form ofa hollow cylinder inserted in the cylinder 10.

The valve element 920 includes a body 921 in the form of a steppedhollow cylinder inserted in the cylinder 10, and a valve portion 922 isformed at an upstream end of the body 921, for being removably seated onthe valve seat 12, with a refrigerant passage 924 axially extendingthrough the body 921 to allow passage of refrigerant.

The refrigerant passage 924 has a stepped portion 925 which is expandedfrom the upstream side to the downstream side, and into the expandedside of the stepped portion 925 there is inserted an inner shaft member930 which functions as a restriction mechanism. In the presentembodiment, the stepped portion 925 is disposed at a location downstreamof the guided portion 23, and the inner shaft member 930 is formed to beaxially shorter than the inner shaft member 30 of the first embodiment.

Further, as shown in FIG. 18, a portion of a side wall slightlydownstream of the stepped portion 925 of the valve element 920 is formedwith a communication hole 941 communication between the inside andoutside of the restriction passage 924.

Next, the pressure-cancelling structure of the expansion device 901 isthe same as that of the first embodiment in that the resultant of thepressure received at the valve-closing pressure-receiving surface 927 ofthe stepped portion 925 and the elastic force of the spring 18 actsagainst the refrigerant pressure received at the valve-opening pressurereceiving surface 26.

Next, the relief mechanism of the expansion device 901 will bedescribed.

As shown in FIGS. 17A and 17C, in the expansion device 901, when thevalve element 920 is seated, the communication hole 941 is opened, whichallows part of the refrigerant flowing through the refrigerant passage924 to escape into another flow passage, and when the differentialpressure across the expansion device 901 has become equal to or higherthan a predetermined value to cause the valve portion 922 to start to bemoved away the valve seat 12, the upstream end of the inner shaft member930 closes the communication hole 941. Then, as soon as the upstream endof the valve element 920 is removed from the small pipe portion 13, mostof the refrigerant flowing in from the upstream side is allowed toescape through a gap between the valve portion 922 and the valve seat12, and flow downstream via the refrigerant passage formed between thevalve element 920 and the cylinder 10 and the plurality of slots 17 b ofthe stopper 17. This prevents an abnormal rise in the refrigerantpressure inside the expansion device 901.

FIG. 19 is an explanatory view explanatory view showing the relationshipbetween the differential pressure across the expansion device 901 andthe opening area of the refrigerant passage(s) thereof.

As shown in FIG. 19, so long as the valve element 920 is seated on thevalve seat 12 (state shown in FIG. 17A), even if the differentialpressure rises, the opening area is held at the sum of thecross-sectional area of the refrigerant passage 924 and that of thecommunication hole 942. Then, when the differential pressure becomeshigher than a predetermined value, the communication hole 941 starts tobe closed, and therefore the cross-sectional area is once decreased(state shown in FIG. 17B). When the differential pressure further risesthereafter, the upstream end of the valve element 920 is removed fromthe small pipe portion 13, which instantly increases the opening area inresponse to a change in the differential pressure (state shown in FIG.17C).

As described above, in the expansion device 901 according to the presentembodiment, e.g. by once stopping the escape of the refrigerant flowingin from the upstream side to once decrease the opening area, the flowcharacteristics representative of relationship between the differentialpressure of the expansion device 901 and the opening area of therefrigerant passage(s) thereof can be set differently from those of thefirst embodiment.

Further, the cooling performance of the expansion device 901 can be alsoenhanced e.g. by increasing the degree of supercooling (subcooling) byonce decreasing the opening area to thereby temporarily decrease theflow rate of the refrigerant.

Tenth Embodiment

Next, a tenth embodiment of the present invention will be described. Thepresent embodiment is an application of the configuration of the ninthembodiment to that of the second embodiment. FIGS. 20A to 20C arecross-sectional views of an expansion device according to the presentembodiment, and FIG. 21 is a cross-sectional view taken on line I-I ofFIG. 20A. It should be noted that since most of the components of theexpansion device according to the present embodiment are similar tothose of the second embodiment, components similar to those of thesecond embodiment will be designated by identical reference numerals,and description thereof is omitted.

As shown in FIG. 20A, the expansion device 1001 comprises a cylinder inthe form of a hollow cylinder 210, and a valve element 1020 in the formof a hollow cylinder inserted in the cylinder 210.

As shown in FIG. 21 as well, a portion of the side wall of the valveelement 1020 at a location opposed to the space portion 241 on thedownstream side of the valve portion 222 is formed with a communicationhole 1041 which communicates between the inside and the outside of therefrigerant passage 224.

Next, the relief mechanism of the expansion device 1001 will bedescribed.

As shown in FIGS. 20A to 20C, in the expansion device 1001, when thevalve element 1020 is seated, the communication hole 1041 is opened,which allows part of the refrigerant flowing through the refrigerantpassage 224 to be introduced into the refrigerant passage formed betweenthe piping 50 and the cylinder 210 via the space portion 241 and thecommunication holes 214 a, to flow downstream. Then, when thedifferential pressure across the expansion device 1001 has become equalto or higher than a predetermined value to cause the valve portion 222to start to be moved away the valve seat 212, the valve element 1020 ismoved downstream, whereby the communication hole 1041 is closed by theguide pipe portion 215. Then, when the upstream end of the valve element1020 is removed from the valve seat portion 213, most of the refrigerantflowing in from the upstream side is allowed to escape via a gap createdbetween the valve portion 222 and the valve seat 212, to flowdownstream. This prevents an abnormal rise in the refrigerant pressureinside the expansion device 1001.

As described above, in the expansion device 1001 according to thepresent embodiment, with the provision of the communication hole 1041,the refrigerant flowing in from the upstream side is allowed to escapein a stepwise manner. As a result, the flow characteristicsrepresentative of the relationship between the differential pressureacross the expansion device 1001 and the opening area of the refrigerantpassage(s) of the same can be set differently from those of the secondembodiment.

Further, the cooling performance of the expansion device 1001 can bealso enhanced e.g. by increasing the degree of supercooling (subcooling)by once decreasing the opening area to thereby temporarily decrease theflow rate of the refrigerant.

Eleventh Embodiment

Next, an eleventh embodiment of the present invention will be described.The present embodiment is an application of the configuration of theninth embodiment to a part of the configuration similar to thecorresponding part of the seventh embodiment. FIGS. 22A to 22C arecross-sectional views of an expansion device according to the presentembodiment, and FIG. 23 is a cross-sectional view taken on line J-J ofFIG. 22A. It should be noted that components similar to those of theseventh embodiment will be designated by identical reference numerals,and description thereof is omitted.

As shown in FIG. 22A, the expansion device 1101 comprises a first reliefmechanism 710 inserted in a upstream part of the cylinder 702, and asecond relief mechanism 1220 inserted in a downstream part of the same.

The second relief mechanism 1220 comprises a second valve element 1120,and a stopper 750.

The second valve element 1120 has a body in the form of a stepped hollowcylinder. An upstream end of the body is reduced in a tapered manner,and from the forward end of the reduced portion axially extends a guidedportion 1122, and a downstream end of the same is formed with a flange1123 which extends radially outward. The guided portion 1122 is insertedin the stopper 750 in the form of a hollow cylinder such that it isslidably held therein, and a stepped portion 1125 formed inside thetapered portion. The cross-section of the downstream side of the steppedportion 1125 is larger than that of the passage cross-section of thestopper 750. Further, the outer surface of the tapered portion forms avalve portion 1121 which can be seated on the valve seat 752 on thedownstream end of the stopper 750.

Further, as also shown in FIG. 23, a portion of the side wall of theguided portion 1122 in the vicinity of the tapered portion is formedwith a communication hole 1141 that communicates between the inside andthe outside of the refrigerant passage 1124. On the other hand, thedownstream end of the valve element 1120 has a tapered shape the outerdiameter of which decreases downstream, and is in abutment with the endface of the stopper 17. The refrigerant passage formed between the valveelement 1120 and the cylinder 702 communicates with the slots 17 b. Aspring 1118 is interposed between the flange 1123 and the downstream endface of the stopper 750, for urging the second valve element 1120 in thedownstream direction.

Next, the relief mechanism of the expansion device 1101 will bedescribed.

As shown in FIGS. 22A to 22C, in the expansion device 1101, when thedifferential pressure across the expansion device 1101 is lower than thesecond predetermined value, the valve element 1120 is not seated, sothat the communication hole 1141 is made open, to allow part of therefrigerant flowing through the refrigerant passage 1124 to beintroduced into the refrigerant passage formed between the valve element1120 and the cylinder 702 via the communication hole 1141, and flowdownstream via the outside of the flange 1123 and the slots 17 b. Then,when the differential pressure has become equal to or higher than thesecond predetermined value to cause the valve element 1121 to start tobe moved toward the valve seat 752, the second valve element 1120 ismoved upstream, so that the stopper 750 starts to close thecommunication hole 1141. When the valve element 1121 is seated on thevalve seat 752, the communication hole 1141 is completely closed.

Further, when the differential pressure has become equal to or higherthan the first predetermined value larger than the second predeterminedvalue, the first relief mechanism 710 operates as described hereinabove.More specifically, the valve portion 22 of the valve element 20 is movedaway from the valve seat 12, to allow most of refrigerant flowing infrom the upstream side to escape through a gap between the valve portion22 and the valve seat 12, and flow downstream through a refrigerantpassage formed between the first valve element 20 and the cylinder 702,and refrigerant passages formed between the cutout portion 753 and thecylinder 702 and between the valve element 1120 of the second reliefmechanism 1220 and the cylinder 702. This prevents an abnormal rise inthe refrigerant pressure inside the expansion device 1101.

FIG. 24 is an explanatory view showing the relationship between thedifferential pressure across the expansion device 1101 and the openingarea of the refrigerant passage(s) thereof.

As shown in FIG. 24, before the second valve element 1120 is seated onthe valve seat 752, even if the differential pressure rises, the openingarea is held at the sum of the cross-sectional area of the refrigerantpassage 1124 and that of the communication hole 1141 (state shown inFIG. 22A). Then, when the differential pressure becomes higher than asecond predetermined value, the communication hole 1141 starts to beclosed to once decrease the area of the opening, and when thecommunication hole 1141 is completely closed, the opening area is heldconstant again (state shown in FIG. 22B). Thereafter, when thedifferential pressure across the expansion device 1101 further rises,the valve portion 22 of the first relief mechanism 710 is removed fromthe valve seat 12, which instantly increases the opening area inresponse to a change in the differential pressure across the expansiondevice 1101(state shown in FIG. 22C).

As described above, in the expansion device 1101 according to thepresent embodiment, with the provision of the communication hole 1141,the refrigerant flowing in from the upstream side is allowed to escapein a stepwise manner. As a result, the flow characteristicsrepresentative of the relationship between the differential pressureacross the expansion device 1101 and the opening area of the refrigerantpassage(s) of the same can be set differently from those of the seventhembodiment.

Further, it is possible to enhance the cooling performance of theexpansion device 1101 as well by once decreasing the opening area totemporarily decrease the flow rate of refrigerant, to thereby enhancethe supercooling degree.

Twelfth Embodiment

Next, a twelfth embodiment of the present invention will be described.FIGS. 25A and 25B are longitudinal cross-sectional views of an expansiondevice according to the present embodiment. FIGS. 26A and 26B aretransverse cross-sectional views of the expansion device, in which FIG.26A is a cross-sectional view taken on line K-K of FIG. 25A, and FIG.26B is a cross-sectional view taken on line L-L of FIG. 25A. It shouldbe noted that most of the configuration of the expansion deviceaccording to the present embodiment is similar to that of the firstembodiment, and therefore description thereof is omitted by designatingsimilar components with identical reference numerals.

As shown in FIG. 25A, in the expansion device 1201, an inner shaftmember 1230 is configured as a solid member having a cylindrical shape,which has a downstream end thereof fixed to a stopper 1217, referred tohereinafter. As shown in FIG. 26A as well, the outer diameter of theinner shaft member 1230 is smaller than the inner diameter of a steppedportion 25 of the valve element 20 by a predetermined amount, whereby agap 1225 is formed between the inner shaft member 1230 and the innerwall of the valve element 20. This gap 1225 communicates with therefrigerant passage 24 and functions as the restriction mechanism.

Further, the stopper 1217 has a shape similar to that of the stopper 17of the first embodiment, but a pair of slots 1217 a are provided inupper and lower halves of the bottom thereof as viewed in FIG. 26B, anda fixing portion 1217 b having a circular shape is formed between theslots 1217 a, for fixing one end of the inner shaft member 1230 thereto.

Next, the relief mechanism of the expansion device 1201 will bedescribed.

As shown in FIGS. 25A and 25B, in the expansion device 1201, the valveelement 20 is seated on the valve seat 12 when the differential pressurethereacross is lower than a predetermined value. Therefore, when therefrigerant flowing in from the upstream side is introduced into therefrigerant passage 24, it is decompressed as it passes through the gap1225, and flows downstream via the slots 1217 a.

Then, when the differential pressure across the expansion device 1201has become equal to or larger than the predetermined value to cause thevalve portion 22 to be moved away from the valve seat 12, most of therefrigerant flowing in from the upstream side is allowed to escapethrough the refrigerant passage formed between the valve element 20 andthe cylinder 10 and flow downstream.

In the expansion device 1201 described above, the inner shaft member1230 is fixed to the stopper 1217, which makes it possible to hold thegap 1225 substantially constant, thereby securing the repeatability ofthe refrigerant flow.

When the repeatability of the refrigerant flow does not matter, theinner shaft member 1230 need not be fixed to the stopper 1217.

Thirteenth Embodiment

Next, a thirteenth embodiment of the present invention will bedescribed. FIGS. 27A to 27C are cross-sectional views of an expansiondevice according to the present embodiment. FIG. 27C is across-sectional view taken on line M-M of FIG. 27A. It should be notedthat most of the configuration of the expansion device according to thepresent embodiment is similar to that of the eleventh embodiment, andtherefore description thereof is omitted by designating similarcomponents with identical reference numerals.

As shown in FIG. 27A, in the expansion device 1301, the valve element1320 has a structure corresponding to the second valve element 1120 ofthe eleventh embodiment, but in this structure, the communication hole1141 is not formed, and a guided portion 1122 is inserted into the smallpipe portion 13 such that it is axially slidably supported therein.Further, the downstream end of the valve element 1320 forms a valveportion 1321, and is configured such that it can be seated on theupstream end face (valve seat) of a stopper 17 disposed on thedownstream side. Further, a spring 1118 is interposed between a flange1123 of the valve element 1320 and a stepped portion of the cylinder1310, for urging the valve element 1320 in the downstream direction.

Further, as shown in FIG. 27C as well, on the downstream side of thevalve element 1320, an inner shaft member 1330 in the form of a cylinderis inserted which has a cutout portion 1330 a formed by cutting off aside portion along the axis thereof while leaving a downstream enduncut, whereby a refrigerant passage 1331 is formed between the cutoutportion 1330 a and the inner surface of the valve element 1320.

Next, the relief mechanism of the expansion device 1301 will bedescribed.

As shown in FIGS. 27A and 27B, in the expansion device 1301, the valveelement 1320 is seated on the upstream end face of the stopper 17 whenthe differential pressure thereacross is lower than a predeterminedvalue. Therefore, when the refrigerant flowing in from the upstream sideis introduced into the refrigerant passage 1124, it is decompressed bypassing through the restriction extending through the inner shaft member1330, and flows downstream via the through hole 17 a.

Then, when the differential pressure across the expansion device 1301has become equal to or larger than the predetermined value to cause thevalve portion 1321 to be moved away from the stopper 17, the refrigerantpassage 1331 is made open to the cylinder 1310, to thereby allow most ofthe refrigerant flowing in from the upstream side to escape downstreamthrough the refrigerant passage 1331, between the inner shaft member1330 and the cylinder 1310, and the slots 17 b.

Fourteenth Embodiment

Next, a fourteenth embodiment of the present invention will bedescribed. FIGS. 28A to 28C are cross-sectional views of an expansiondevice according to the present embodiment. FIG. 29 is a cross-sectionalview taken on line N-N of FIG. 28A. It should be noted that most of theconfiguration of the expansion device according to the presentembodiment is similar to that of the thirteenth embodiment, andtherefore description thereof is omitted by designating similarcomponents with identical reference numerals.

As shown in FIGS. 28A and 29, the expansion device 1401 includes aninner shaft member 1430 which is a modification of the inner shaftmember 1330 in the thirteenth embodiment in which a groove 1430 a havinga predetermined width is formed in the inner shaft member 1330 at alocation circumferentially shifted from the cutout portion 1330 a, inside view. The groove 1430 a extends further downstream with respect tothe cutout portion 1330 a by a predetermined amount, thereby forming arefrigerant passage 1432 having a smaller passage cross-section thanthat of the refrigerant passage 1331, between the groove 1430 a and theinner surface of the valve element 1320.

Next, the relief mechanism of the expansion device 1401 will bedescribed.

As shown in FIGS. 28A to 28C, in the expansion device 1401, when thedifferential pressure across the expansion device 1401 has become equalto or higher than a predetermined value to cause the valve portion 1321to start to be moved away the stopper 17, first, the refrigerant passage1432 is made open to the cylinder 1310 to thereby allow part ofrefrigerant flowing in from the upstream side to escape downstreamthrough the refrigerant passage 1432, a flow passage formed between theinner shaft member 1430 and the cylinder 1310, the slots 17 b. Then,when the differential pressure becomes still higher, the valve element1320 is moved further upstream to open the refrigerant passage 1331, tothereby allow most of the refrigerant flowing in from the upstream sideto escape downstream via the refrigerant passage 1331, the flow passagebetween the inner shaft 1430 and the cylinder 1310, and the slots 17 b.

Fifteenth Embodiment

Next, a fifteenth embodiment of the present invention will be described.FIGS. 30A to 30C are longitudinal cross-sectional views of an expansiondevice according to the present embodiment. It should be noted that mostof the configuration of the expansion device according to the presentembodiment is similar to that of the thirteenth embodiment, andtherefore description thereof is omitted by designating similarcomponents with identical reference numerals.

As shown in FIG. 30A, a valve element 1520 of the expansion device 1501has a guided portion 1442 as a modification of the side wall of theguided portion 1122, through which is formed a communication hole 1521communicating between the inside and outside of the refrigerant passage1124, at a location in the vicinity of the tapered portion on theupstream side of the valve element 1320 in the thirteenth embodiment.

Next, the relief mechanism of the expansion device 1501 will bedescribed.

As shown in FIGS. 30A and 30C, in the expansion device 1501, when thedifferential pressure across the expansion device 1501 is lower than thesecond predetermined value, the communication hole 1521 is made open, toallow part of the refrigerant flowing through the refrigerant passage1124 to be introduced into the refrigerant passage formed between thevalve element 1520 and the cylinder 1310 via the communication hole1521, and flow downstream via the outside of the flange 1123 and theslots 17 b. Then, when the differential pressure has become equal to orhigher than the second predetermined value, to cause the valve element1520 to be moved upstream, the small pipe portion 13 closes thecommunication hole 1521.

Further, when the differential pressure has become equal to or higherthan the first predetermined value larger than the second predeterminedvalue, the valve element 1520 is moved further upstream whereby therefrigerant passage 1331 is made open, to thereby allow most ofrefrigerant flowing in from the upstream side to escape through therefrigerant passage 1331, a flow passage between the inner shaft member1330 and the cylinder 1310, and the slots 17 b.

Sixteenth Embodiment

Next, a sixteenth embodiment of the present invention will be described.FIGS. 31A and 31B are cross-sectional views of an expansion deviceaccording to the present embodiment. It should be noted that theexpansion device according to the present embodiment has such aconfiguration as a combination of the twelfth embodiment and thethirteenth embodiment, and therefore description of components of thepresent embodiment similar to those of these embodiments is omittedwhile designating the similar components with identical referencenumerals.

As shown in FIG. 31A, in the expansion device 1601, an inner shaftmember 1630 is configured as a solid member in the form of a cylinder,which has a downstream end thereof fixed to a stopper 1217. The diameterof the inner shaft member 1630 is smaller than the inner diameter of thestepped portion 1125 of the valve element 1320 by a predeterminedamount, whereby a gap 1625 is formed between the inner shaft member 1630and the inner wall of the valve element 1320. This gap 1625 communicateswith the refrigerant passage 1124 and functions as the restrictionmechanism. Further, the inner shaft member 1630 is formed with a cutoutportion 1630 a which is formed by cutting off a portion thereof alongthe axis, while leaving a downstream end thereof uncut, whereby a flowpassage 1631 is formed between the cutout portion 1630 a and the innersurface of the valve element 1320.

Next, the relief mechanism of the expansion device 1601 will bedescribed.

As shown in FIGS. 31A and 31B, in the expansion device 1601, when thedifferential pressure thereacross is lower than a predetermined value,the refrigerant flowing in from the upstream side is decompressed bypassing through the gap 1625, and flows downstream via slots 1217 a.

Then, when the differential pressure across the expansion device 1601has become equal to or larger than the predetermined value to cause thevalve portion 1321 to be moved away from the stopper 1217, most of therefrigerant flowing in from the upstream side is allowed to escapedownstream through the refrigerant passage 1631, a flow passage betweenthe inner shaft member 1630 and the cylinder 1310, and the slots 17 b.

Seventeenth Embodiment

Next, a seventeenth embodiment of the present invention will bedescribed. FIGS. 32A and 32B are longitudinal cross-sectional views ofan expansion device according to the present embodiment. Further, FIGS.33A and 33B are transverse cross-sectional views of the expansiondevice, in which FIG. 33A is a cross-sectional view taken on line O-O ofFIG. 32A, and FIG. 33B is a view taken from a direction of P of FIG.32A. It should be noted that components similar to those of the firstembodiment will be designated by identical reference numerals, anddescription thereof is omitted.

The present embodiment realizes a configuration that enhances theaccuracy of the pressure cancellation. More specifically, similarly tothe first embodiment as shown in FIG. 2, in a configuration where thepressure-receiving surface of the valve portion 22 has a tapered shape,the effective pressure-receiving area of the valve element 20 tends tobecome smaller as the valve element 20 is moved away from the valve seat12. As a result, actually, as designated by dotted line in FIG. 35, witha rise in the differential pressure, the rate of increase in the openingarea is lowered to cause the balance of the pressure cancellation to belost, or degrade the relieving operation. The expansion device 1701according to the present embodiment solves the problem.

As shown in FIG. 32A, the expansion device 1701 comprises a cylinder 10in the form of a hollow cylinder, and a valve element 1270 in the formof a hollow cylinder inserted in the cylinder 10. A large pipe portion14 of the cylinder 10 has a stopper 1717 in the form of a disk fixedthereto at a location in the vicinity of the downstream end thereof, anda spring 18 is interposed between the stopper 1717 and the valve element1720, for urging the valve element 1720 toward a valve seat 12 (in thevalve-closing direction).

The valve element 1720 comprises a body in the form of a stepped hollowcylinder inserted in the cylinder 10, a valve portion 1721 in the formof a hollow cylinder which can be removably seated on the valve seat 12,and a guided portion 1722 in the form of a stepped hollow cylinderdisposed on the downstream side of the valve portion 1721.

The upstream end of the valve portion 1721 is provided with a taperedportion the outer diameter of which decreases upstream, and when thevalve portion 1721 is seated, the foremost end of the tapered portion1721 is inserted into the small pipe portion 13 by a predeterminedamount.

As shown in FIG. 33A, the guided portion 1722 comprises a body 1723having a generally hexagonal cross-section, and a reduced pipe portion1724 in the form of a hollow cylinder formed continuous with thedownstream side of the body 1723. Each vertex portion of the body 1723is configured to have an arcuate shape extending along the innerperipheral surface of the large pipe portion 14, and refrigerantpassages are formed between the vertex portions, which allow passage ofrefrigerant. The valve element 1720 is stably moved forward and backwardwithin the cylinder 10, with the vertex portions sliding along the innersurface of the large pipe portion 14. Further, the reduced pipe portion1724 has one end of the spring 18 fitted thereon.

The upstream end of the body 1723 is slightly expanded, and thedownstream end of the valve portion 1721 is press-fitted therein.Therefore, a space portion S1 is formed between the valve portion 1721and the reduced pipe 1724 of the guided portion 1722. In this spaceportion S1, a shaft-like member 1730 in the form of a stepped cylinder,referred to hereinafter, is partially inserted.

The stopper 1717 is, as shown in FIG. 33B as well, formed with a screwhole 1717 a extending through the center thereof. Around the screw hole1717 a, there are formed three elongated holes 1717 b at equal intervals(of 120 degrees). The flow passage area as the sum of the these threeelongated holes 1717 b is sufficiently larger than that of the flowpassage formed by a gap created between the valve portion 1721 and thevalve seat 12, which prevents pressure loss of the refrigerant fromoccurring in the elongated holes 1717 b. The stopper 1717 is equippedwith an adjusting mechanism, that is, the stopper 1717 has an outerperiphery formed with an external thread, and a downstream end of thecylinder 10 is formed with an internal thread mating with the externalthread. By adjusting the amount of screwing of the stopper 1717 into thecylinder 10, the position of the stopper 1717 is adjusted, whereby theelastic force of the spring 18 can be adjusted. Further, through thescrew hole 1717 a of the stopper 1717, there is inserted a set screw1740 (engaging member) with a slotted head or a hexagon socket byscrewing, such that a foremost end thereof holds the downstream end faceof the shaft-like member 1730. By adjusting the amount of screwing ofthe set screw 1740 with respect to the stopper 1717, the position of theset screw 1740 is adjusted, whereby the axial position of the shaft-likemember 1730 within the cylinder 10 can be adjusted.

FIGS. 34A to 34C are explanatory views showing the configuration of therestriction mechanism according to the present embodiment, in which FIG.34A is a partial expanded cross-sectional view showing the configurationof the vicinity of the valve element 1720, and FIGS. 34B and 34C showexpanded views of Q portion in FIG. 34A.

As shown in 34A, the shaft-like member 1730 has an upstream end thereofformed with a tapered portion 1731 the cross-section of which increasesupstream. A restriction passage is formed by a gap between the taperedsurface of the tapered portion 1731 and an inner peripheral edge 1724 aof the reduced pipe portion 1724. As shown in FIG. 34B, so long as thevalve element 1720 is seated on the valve seat 12, the restrictionpassage holds the gap at a predetermined value c1 which realizes thepassage cross-section of the normal restriction mechanism. Therefore,the refrigerant pressure is high on the upstream side of the gap, andlow on the downstream side of the same. However, as shown FIG. 34C, whenthe valve element 1720 is moved away from the valve seat 12, the gap hasbecome equal to a value c2 larger than the predetermined value c1, whichmakes it possible to allow the refrigerant to flow at a larger flowrate, but on the other hand, the function of the restriction mechanismis lowered. It should be noted that the size of the restriction passagein the closed state of the valve can be freely set by adjusting theposition of the shaft-like member 1730 using the adjusting mechanismdescribed above.

Further, the upstream end face of the shaft-like member 1730 is formedwith a groove 1732 extending diametrically therethrough, as shown inFIG. 33A, and the remaining portion of the end face is capable ofholding the valve portion 1721, and hence the valve element 1720 fromthe downstream side. Further, since the groove 1732 communicates withthe refrigerant passage extending through the valve portion 1721, evenwhen the valve portion 1721 is engaged with the shaft-like member 1730,the refrigerant can be allowed to flow through the communication passageformed by the groove 1732, the space portion S1, and the reduced pipeportion 1724.

Next, the pressure-cancelling structure of the expansion device 1701will be described.

In the expansion device 1701, as shown in FIG. 34B, to receive thehigh-pressure refrigerant introduced from the upstream side into therefrigerant passage in the small pipe portion 13, a valve-openingpressure-receiving surface is formed by a portion 1751 of the upstreamend face of the valve portion 1721, which is inserted into the smallpipe portion 13, and an upstream end face 1752 of the reduced pipeportion 1724 of the guided portion 1722, and a valve-closingpressure-receiving surface is formed by the downstream end face 1753 ofthe valve portion 1721. Further, the inner diameter of the reduced pipeportion 1724 is made smaller than that of the small pipe portion 13 (seedotted lines in FIG. 34B) such that the pressure-receiving area of theentire valve-opening pressure-receiving surface becomes larger than thepressure-receiving area of the entire valve-closing pressure-receivingsurface. That is, the refrigerant introduced into the space SI withinthe valve element 1720 acts to urge the valve element 1720 in thevalve-closing direction (rightward as viewed in FIG. 34A) to therebycancel part of the refrigerant pressure acting on the valve element 1720in the valve-opening direction. Therefore, the resultant of the pressurereceived at the valve-closing pressure-receiving surface and the elasticforce of the spring 18 acts against the refrigerant pressure received atthe valve-opening pressure-receiving surface.

Next, the relief mechanism of the expansion device 1701 will bedescribed.

As shown in FIGS. 32A and 32B, in the expansion device 1701, when thedifferential pressure across the expansion device 1701 has become equalto or higher than a predetermined value to cause the valve portion 1721to be moved away the valve seat 12, most of refrigerant flowing in fromthe upstream side is allowed to escape through a gap between the valveportion 1721 and the valve seat 12, and flow downstream through arefrigerant passage formed between the valve element 1720 and thecylinder 10 and the elongated holes 1717 b of the stopper 1717. Thisprevents an abnormal rise in the refrigerant pressure inside theexpansion device 1701.

FIG. 35 is an explanatory view showing the relationship between thedifferential pressure across the expansion device 1701 and the openingarea of the refrigerant passage(s) thereof.

As shown in FIG. 35, so long as the valve element 1720 is seated on thevalve seat 12 (state shown in FIG. 32A), even if the differentialpressure rises, the opening area is held constant by being limited bythe restriction passage. Then, when the differential pressure becomeshigher than a predetermined value, the valve element 1720 is moved awayfrom the valve seat 12 to allow the refrigerant to escape into theoutside refrigerant passage to relieve the pressure. Thus, the openingarea is instantly increased (state shown in FIG. 32B). In this case, itis possible to prevent or suppress the lowering in the rate of increasein the opening area which might occur as the differential pressureacross the expansion device 1701 rises as shown by a dotted line in FIG.35, whereby it is possible to prevent the characteristics of theexpansion device from being changed due to lowering in the receivedpressure, as shown by a solid line, thereby enabling the refrigerant toescape such that the refrigerant pressure is sufficiently relieved.

It is presumed that this is because a change (decrease) in the effectivepressure-receiving area of the valve element 1720 and a change(increase) in the effective pressure-receiving area of the reduced pipeportion 1724 are cancelled each other, which makes it possible to cancelvariation in the received pressure caused by the lift of the valveelement 1720.

As described above, in the expansion device 1701 U according to thepresent embodiment, since the pressure-cancelling structure cancels partof the refrigerant pressure, a small-sized spring can be employed forthe spring 18. As a result, it is possible to make the entire expansiondevice 1701 compact in size.

Further, when the differential pressure across the expansion device 1701has become equal to or higher than the predetermined value, therefrigerant flowing in from the upstream side can be allowed to escapeinto the other flow passage than the normal refrigerant passageextending by way of the restriction passage, which makes it possible toprevent an abnormal rise in the refrigerant pressure inside theexpansion device 1701, to thereby prevent breakage or the like of theinternal components.

Further, as described above, the passage cross-section of therestriction passage on the downstream side is increased according to thevalve opening condition of the valve element 1720. This preventsvariation in the characteristics caused by the decrease in the receivedpressure, maintains the balance of the pressure cancellation, andimproves the relieving operation.

Although in the present embodiment, the inner diameter of the reducedpipe portion 1724 is smaller than that of the small pipe portion 13,this is not limitative, but these inner diameters may be made equal toeach other. Even with this configuration, due to the configuration inwhich the passage cross-section of the restriction passage on thedownstream side is increased, it is possible to expect the effects ofmaintaining the balance of the pressure cancellation and the like.

Further, there may be provided a guide means for stably holding theshaft-like member 1730 within the cylinder 10. For example, theshaft-like member 1730 may be formed with a plurality of guide portionswhich extend radially outward from the outer peripheral surface of anupstream end thereof, so as to be guided by the inner peripheral surfaceof the guided portion 1722 of the valve element 1720.

Eighteenth Embodiment

Next, an eighteenth embodiment of the present invention will bedescribed. FIGS. 36A and 36B are longitudinal cross-sectional views ofan expansion device according to the present embodiment. Further, FIGS.37A and 37B are transverse cross-sectional views of the expansiondevice, in which FIG. 37A is a cross-sectional view taken on line R-R ofFIG. 36A, and FIG. 37B is a view taken from a direction of S of FIG.36A. It should be noted that components similar to those of the firstembodiment will be designated by identical reference numerals, anddescription thereof is omitted.

As shown in FIG. 36A, the expansion device 1801 comprises a cylinder 10in the form of a hollow cylinder, a valve element 1820 in the form of ahollow cylinder inserted in the cylinder 10, and a ball valve seat 1830in the form of a ball supported within the cylinder 10. In the vicinityof the downstream end of the large pipe portion 14 of the cylinder 10, astopper 1817 in the form of a bottomed hollow cylinder is secured, withthe ball valve seat 1830 being interposed between the stopper 1817 andthe valve element 1820. Further, a spring 18 is interposed between thedownstream end face of the small pipe portion 13 and the valve element1820, for urging the valve element 1820 toward the ball valve seat 1830(in the valve-closing direction).

The valve element 1820 has a body in the form of a stepped hollowcylinder which is expanded downstream in two stages. A hollowcylindrical portion as a central part of the body forms a body portion1821, with a reduced pipe portion 1822 formed on the upstream side ofthe body portion 1821 by reducing the diameter of a correspondingportion of the body, and a guide portion 1823 formed on the downstreamside of the body portion 1821 by increasing the diameter of acorresponding portion of the body. Further, a valve portion 1824 in theform of a hollow cylinder is formed by a downstream end of the bodyportion 1821.

The reduced pipe portion 1822 has an outer diameter slightly smallerthan that of the small pipe portion 13, and movably inserted in thesmall pipe portion 13. The gap between the reduced pipe portion 1822 andthe small pipe portion 13 forms a restriction passage (restrictionmechanism). The junction of the reduced pipe portion 1822 and the bodyportion 1821 has a tapered shape in which the outer diameter thereofdecreases toward the upstream end of the body.

As shown in FIG. 37A, the guide portion 1823 has an approximatelyhexagonal cross-section, and vertex portions each have an arcuate shapeextending along the inner peripheral surface of the large pipe portion14, defining refrigerant passages therebetween which allow passage ofrefrigerant. The vertex portions of the guide portion 1823 are slidalong the inner surface of the large pipe portion 14, whereby the valveportion 1820 can be stably moved forward and backward within thecylinder. Further, the inside of the guide portion 1823 has a taperedshape in which the cross-section thereof is increased downstream, and adownstream end face of the tapered portion facing downstream can receivethe ball valve seat 1830 in a manner covering an upstream portion of theball valve seat 1830. As shown in FIG. 36A, when the valve portion 1824of the valve element 1820 is seated on the ball valve seat 1830, apredetermine gap is formed between the tapered portion and the ballvalve seat 1830. At this time, the ball valve seat 1830 is supported bythe upstream end face of the stopper 1817 and the valve portion 1824 ina manner sandwiched therebetween. The aforementioned spring 18 is fittedon the body portion 1821, and interposed between an upstream end face ofthe guide portion 1823 and a downstream end face of the small pipeportion 13.

As shown in FIG. 37B as well, the stopper 1817 is formed with threeslots 1817 a around the center thereof at equal intervals (of 120degrees), which form refrigerant passages. The cross-sectional area of aflow passage as the sum of the these three slots 1817 a is sufficientlylarger than that of a flow passage formed by a gap created between thevalve portion 1824 and the ball valve seat 1830, which prevents pressureloss of the refrigerant from occurring in the slots 1817 a. The stopper1817 is equipped with an adjusting mechanism, that is, the stopper 1817has an outer periphery formed with an external thread, and a downstreamend of the cylinder 10 is formed with an internal thread mating with theexternal thread. By adjusting the amount of screwing of the stopper 1817into the cylinder 10, the position of the ball valve seat 1830supporting on the upstream side is adjusted.

Next, the pressure-cancelling structure of the expansion device 1801will be described,.

In the expansion device 1801, an upstream end face of the reduced pipeportion 1822 forms a valve-closing pressure-receiving surface, and adownstream facing surface of the tapered portion at the boundary of thereduced pipe portion 1822 and the body portion 1821 within the valveelement 1820 forms a valve-opening pressure-receiving surface larger inpressure-receiving area than the valve-closing pressure-receivingsurface. That is, the refrigerant introduced from the upstream side actson the valve element 1820 in the valve-closing direction (leftward asviewed in FIG. 36B) to thereby cancel part of the refrigerant pressureacting on the valve element 1820 in the valve-opening direction.Therefore, the resultant of the pressure received at the valve-closingpressure-receiving surface and the elastic force of the spring 18 actsagainst the refrigerant pressure received at the valve-openingpressure-receiving surface.

Next, the relief mechanism of the expansion device 1801 will bedescribed.

As shown in FIGS. 36A and 36B, in the expansion device 1801, when thedifferential pressure across the expansion device 1801 has become equalto or higher than a predetermined value to cause the valve portion 1824to be moved away the ball valve seat 1830, most of refrigerant flowingin from the upstream side is allowed to escape through a gap between thevalve portion 1824 and the ball valve seat 1830, and flow downstreamthrough the slots 1817 a of the stopper 1817. This prevents an abnormalrise in the refrigerant pressure inside the expansion device 1801.

In the expansion device 1801 as well, the relationship between thedifferential pressure thereacross and the opening area of therefrigerant passage(s) is approximately the same as that shown in FIG.35.

That is, so long as the valve element 1820 is seated on the ball valveseat 1830 (state shown in FIG. 36A), even if the differential pressurerises, the opening area is held constant by being limited by therestriction passage formed by the gap between the reduced pipe portion1822 and the small pipe portion 13. Then, when the differential pressurebecomes higher than a predetermined value, the valve element 1820 ismoved away from the ball valve seat 1830 to allow the refrigerant toescape into an inner refrigerant passage to relieve the refrigerantpressure. Thus, the opening area is instantly increased (state shown inFIG. 36B).

As described above, in the expansion device 1801 according to thepresent embodiment as well, since the pressure-cancelling structurecancels part of the refrigerant pressure, it is possible to make theentire expansion device 1801 compact in size.

Further, when the differential pressure across the expansion device 1801has become equal to or higher than a predetermined value, the reliefmechanism prevents an abnormal rise in the differential pressure,thereby making it possible to prevent breakage or the like of theinternal components.

Further, as described above, since the decrease in the effectivepressure-receiving area is small when the valve element 1820 is opened,but on the contrary, the surface thereof urged in the valve-openingdirection is increased, so that it is possible to increase the accuracyof the pressure cancellation, and cause the relieving function tooperate more rapidly. As a result, the differential pressure across theexpansion device before the required maximum valve lift is reached canbe small, so that the pressure load on the entire expansion device canbe reduced to protect the same.

Nineteenth Embodiment

Next, a nineteenth embodiment of the present invention will bedescribed. FIGS. 38A and 38B are longitudinal cross-sectional views ofan expansion device according to the present embodiment. Further, FIGS.39A and 39B are transverse cross-sectional views of the expansiondevice, in which FIG. 39A is a cross-sectional view taken on line T-T ofFIG. 38A, and FIG. 39B is a cross-sectional view taken on line U-U ofFIG. 38A. It should be noted that components similar to those of thefirst embodiment will be designated by identical reference numerals, asrequired, and description thereof is omitted.

As shown in FIG. 38A, the expansion device 1901 comprises a cylinder 10in the form of a hollow cylinder, and a valve element 1920 in the formof a hollow cylinder inserted in the cylinder 10. In the vicinity of thedownstream end of the large pipe portion 14 of the cylinder 10, astopper 1917 in the form of a hollow cylinder is secured. Further, aspring 18 is interposed between the stopper 1917 and the valve element1920, for urging the valve element 1920 toward the small pipe portion 13(in the valve-closing direction).

Further, the downstream end of the small pipe portion. 13 of thecylinder 10 is provided with a guide pipe 1930 in the form of a bottomedhollow cylinder extending downstream from the downstream-side opening ofthe small pipe portion 13. The guide pipe 1930 has its downstream endclosed, and as also shown in FIG. 39A, a side wall thereof in thevicinity of the downstream end thereof is formed with communicationholes 1931 which communicate between the inside and outside of the guidepipe 1930. Further, the guide pipe 1930 has the valve element 1920fitted thereon in a manner slidable thereon, and the downstream end ofthe guide pipe 1930 is formed with a tapered portion 1932 thecross-section of which decreases downstream. The tapered portion 1932forms a valve seat.

The valve element 1920 comprises a valve portion 1921 having a body inthe form of a stepped hollow cylinder inserted in the cylinder 10, and aguided portion 1922 which is guided by the guide pipe 1930 while slidingthereon, and can be held by the downstream facing surface of a steppedportion provided at a boundary between the small pipe portion 13 and thelarge pipe portion 14 of the cylinder 10, i.e. a downstream end face1912 of the small pipe portion 13.

The guided portion 1922 has an upstream portion which has an innerdiameter approximately equal to the outer diameter of the guide pipe1930 and is slidable thereon, whereby the valve element 1920 can bestably moved forward and backward within the cylinder 10. A downstreamportion of the guide pipe 1922 is slightly increased in inner diameterto thereby form a space portion S2. Further, as shown in FIG. 39B, aportion of the upstream end of the guided portion 1922 is formed with aslit 1922 a communicating between the inside and outside of the guidedportion 1922, whereby the high-pressure refrigerant leaked through a gapbetween the guided portion 1922 and the guide pipe 1930 can be allowedto flow downstream.

On the other hand, the valve portion 1921 has a reduced pipe portion1924 extending downstream with a reduced size, and one end of the spring18 is fitted on the reduced pipe portion 1924. An upstream end of thevalve portion 1921 is slightly increased in inner diameter, and thedownstream end of the guided portion 1922 is press-fitted in theupstream end of the valve portion 1921. Therefore, within the valveelement 1920, there is formed a space portion S2 defined by the valveportion 1921, the guided portion 1922, and the guide pipe 1930. Thespace portion S2 communicates with the upstream side via thecommunication holes 1931.

Further, the tapered surface of the tapered portion 1932 of the guidepipe 1930 and an inner peripheral edge 1924 a of the reduced pipeportion 1924 form a restriction passage. When the valve element 1920 isheld on the downstream end face 1912 of the small pipe portion 13, therestriction passage holds the gap at a preset value realizing thepassage cross-section of the normal restriction mechanism. However, whenthe valve element 1920 is moved away from the downstream end face 1912to be fully open, the function of the restriction mechanism is actuallyterminated, but a new refrigerant passage is formed which is increasedin flow passage area. That is, the other refrigerant passage than therefrigerant passage that is open in the closed state of the valve ismade open in an integrating manner.

It should be noted that an adjusting mechanism, described hereinabove,may be provided between the valve portion 1921 and the guided portion1922, for adjusting the positional relationship between the valveportion 1921 and the guided portion 1922, thereby making it possible toset the size of the restriction passage as desired.

The stopper 1917 is equipped with an adjusting mechanism, that is, thestopper 1917 has an outer periphery formed with an external thread, anda downstream end of the cylinder 10 is formed with an internal threadmating with the external thread. By adjusting the amount of screwing ofthe stopper 1917 into the cylinder 10, the position of the stopper 1917is adjusted, whereby the elastic force of the spring 18 can be adjusted.

Next, the pressure-cancelling structure of the expansion device 1901will be described,.

In the expansion device 1901, within the space portion S2, thedownstream facing surface of the guided portion 1922 forms avalve-closing pressure-receiving surface, and on the other hand, theupstream end of the reduced pipe portion 1924 forms a valve-openingpressure-receiving surface which is larger in pressure-receiving areathan the valve-closing pressure receiving surface. Further, the innerdiameter of the reduced pipe portion 1924 is made smaller than that ofthe guided portion 1922 such that the pressure-receiving area of thevalve-opening pressure-receiving surface becomes larger than that of thevalve-closing pressure-receiving surface. That is, the refrigerantintroduced into the space S2 acts on the valve element 1920 in thevalve-closing direction (rightward as viewed in FIG. 38A) to therebycancel part of the refrigerant pressure acting on the valve element 1920in the valve-opening direction. Therefore, the resultant of the pressurereceived at the valve-closing pressure-receiving surface and the elasticforce of the spring 18 acts against the refrigerant pressure received atthe valve-opening pressure-receiving surface.

Next, the relief mechanism of the expansion device 1901 will bedescribed.

As shown in FIGS. 38A and 38B, in the expansion device 1901, when thedifferential pressure across the expansion device 1901 has become equalto or higher than a predetermined value to cause the guided portion 1922to be moved away the downstream end face 1912, the opening area of thegap between the reduced pipe portion 1924 and the guide pipe 1930 isincreased against the urging force of the spring 19, whereby refrigerantflowing in from the upstream side is allowed to escape at an increasedflow rate. This prevents an abnormal rise in the refrigerant pressureinside the expansion device 1901.

FIG. 40 is an explanatory view showing the relationship between thedifferential pressure across the expansion device 1901 and the openingarea of the refrigerant passage(s) thereof.

As shown in FIG. 40, so long as the valve element 1920 is held on thedownstream end face 1912 of the small pipe portion 13 (state shown inFIG. 38A), even if the differential pressure rises, the opening area isheld constant by being limited by the restriction passage. Then, whenthe differential pressure becomes higher than a predetermined value, thevalve element 1920 is moved away from the downstream end face 1912 toallow refrigerant to flow downstream at the increased flow rate. Thus,the opening area is instantly increased (state shown in FIG. 38B). Inthis case, as shown in FIG. 38B, the rate of increase in the openingarea is larger than that of the seventeenth embodiment (FIG. 35).

As described above, in the expansion device 1901 as well, thepressure-cancelling structure and the relief mechanism functioneffectively, and therefore the same advantageous effects as provided bythe first embodiment can be obtained.

Further, in the expansion device 1901 as well, similarly to theeighteenth embodiment, when the valve element 1920 is opened, thereoccurs no decrease in the effective pressure-receiving area, whichenables the balance of the pressure cancellation to be maintained, andimproves the relieving operation. Further, in relieving the refrigerantpressure, the refrigerant passage can be expanded instantly, whichdecreases the differential pressure across the expansion device requiredfor setting the maximum valve lift. Therefore, the pressure load on theentire expansion device can be reduced to thereby protect the same.

Although the preferred embodiments of the present invention have beendescribed heretofore, the present invention is by no means limited toany specific one of the above-described embodiments, but variousmodifications and alterations can be made thereto without departing thespirit and scope of the present invention.

For example, although in the above-described embodiments, the cylinderof each expansion device is directly fixed to the piping 50, by way ofexample, this is not limitative, but the expansion device may beprovided with a casing or the like which accommodates the cylinder, andthe casing or the like may be fixed to the piping.

Further, although in the above embodiments, at least one of the outerperipheral surface of the inner shaft member and the inner peripheralsurface of the valve element inserted therein may be formed with atleast one labyrinth groove.

It should be noted that internal components forming expansion devicesmay be formed e.g. of resin.

The present invention can be applied to any expansion device so long asit is disposed in a flow passage of refrigerant circulating through arefrigeration cycle.

According to the expansion device of the present invention, in the valveelement, part of the refrigerant pressure is cancelled by thepressure-cancelling structure, which makes it possible to reduce theelastic force required of the elastic member that holds the valveelement in a manner acting against the refrigerant pressure. As aresult, it is possible to employ a small-sized elastic member, andthereby make the configuration of the entire expansion device compact insize.

Further, with the compact configuration, the relief mechanism makes itpossible to prevent an abnormal rise in the refrigerant pressure insidethe expansion device, to thereby prevent breakage or the like of theinternal components.

Further, by providing the relief mechanism in two stages, i.e. as thefirst relief mechanism and the second relief mechanism, refrigerantpressure reduction control can be carried out in a more delicate manner.

The foregoing is considered as illustrative only of the principles ofthe present invention. Further, since numerous modifications and changeswill readily occur to those skilled in the art, it is not desired tolimit the invention to the exact construction and applications shown anddescribed, and accordingly, all suitable modifications and equivalentsmay be regarded as falling within the scope of the invention in theappended claims and their equivalents.

1. An expansion device that is disposed in a flow passage of refrigerantcirculating through a refrigeration cycle, for passing the refrigerantintroduced from an upstream side thereof through an internal refrigerantpassage thereof to thereby cause decompression of the refrigerant andallow the decompressed refrigerant to flow downstream, and is equippedwith a relief mechanism that is operable when a differential pressureacross the expansion device has become equal to or higher than apredetermined value, to open a flow passage other than the refrigerantpassage which is closed by a valve element urged by an elastic memberdisposed within the expansion device, to thereby allow at least part ofthe refrigerant flowing in from the upstream side to escape via the flowpassage to flow downstream, the expansion device comprising: apressure-cancelling structure that cancels part of pressure of therefrigerant acting on the valve element in a valve-opening direction. 2.An expansion device that is disposed in a flow passage of refrigerantcirculating through a refrigeration cycle, comprising: a cylinder in theform of a hollow cylinder, the cylinder having a valve seat formed by astepped portion provided inside the hollow cylinder; a valve elementthat has a body in the form of a hollow cylinder, the valve elementbeing movably inserted within the cylinder, and including a valveportion that forms part of the body and can be removably seated on thevalve seat, and a refrigerant passage extending through an inside of thebody to allow passage of the refrigerant; a restriction mechanism thatdecompresses the refrigerant passing through the refrigerant passage; anelastic member that is disposed within the cylinders for urging thevalve element in a valve-closing direction; a pressure-cancellingstructure that cancels at least part of pressure of the refrigerantacting on the valve element in a valve-opening direction, thepressure-cancelling structure comprising a valve-closingpressure-receiving surface that receives pressure of the refrigerantacting on the valve element in the valve-closing direction and has apressure-receiving area which is smaller than a pressure-receiving areaof a valve-opening pressure-receiving surface that receives pressure ofthe refrigerant acting on the valve element in the valve-openingdirection; and a relief mechanism that is operable when a differentialpressure across the expansion device has become equal to or higher thana predetermined value to cause the valve portion to be moved away fromthe valve seat, to allow at least part of the refrigerant flowing infrom an upstream side to escape into a flow passage other than therefrigerant passage extending through the cylinder.
 3. The expansiondevice according to claim 2, wherein, the valve element includes aguided portion that is guided along an inner peripheral surface of thecylinder when the valve element is moved to and away from the valveseat.
 4. The expansion device according to claim 2, wherein the cylinderis directly fixed to an inside of the piping of the refrigeration cycle.5. The expansion device according to claim 3, comprising: a steppedportion in the refrigerant passage of the valve element at which therefrigerant passage is expanded in an upstream-to-downstream direction;an inner shaft member in the form of a hollow cylinder that has aflow-restricting portion formed therein, the flow-restricting portionhaving a cross-section smaller than a cross-section of the refrigerantpassage, and is partially inserted into an expanded side of the steppedportion of the valve element, the inner shaft member protrudingdownstream from the valve element, and functioning as the restrictionmechanism; and a stopper that is fixed to the cylinder, and configuredto be capable of having a downstream end of the inner shaft memberengaged thereat, the stopper being formed with a through hole having across-section larger than a cross-section of the flow-restrictingportion, and wherein an internal space is formed between the inner shaftmember and the stepped portion, and the stepped portion forms thevalve-closing pressure-receiving surface.
 6. The expansion deviceaccording to claim 5, wherein the stopper is formed with at least onesecond through hole other than the through hole, the second through holecommunicating with the flow passage other than the refrigerant passage,and wherein a flow passage area of an entirety of the second throughhole is larger than a flow passage area of a gap formed between thevalve portion and the valve seat when the valve element is opened. 7.The expansion device according to claim 5, wherein the inner shaftmember is supported by the valve element, but not fixed to any part ofan internal structure of the cylinder.
 8. The expansion device accordingto claim 5, wherein the cylinder includes a small pipe portion thatcommunicates with the refrigerant passage when the valve element isseated on the valve seat, and a large pipe portion that has a passagecross-section larger than a passage cross-section of the small pipeportion, and is configured such that the stepped portion is formed bythe small pipe portion and the large pipe portion, and wherein thepressure-cancelling structure is formed by making the passagecross-section of the small pipe portion larger than a cross-section ofthe expanded side of the stepped portion of the valve element.
 9. Theexpansion device according to claim 5, wherein the guided portioncomprises a plurality of protruding portions extending from the bodytoward an inner surface of the cylinder, the protruding portionsdefining therebetween refrigerant flow passages that allow passage ofthe refrigerant, and on the other hand, the stopper has at least onesecond through hole formed around the through hole, the second throughhole communicating with the refrigerant flow passages, and wherein whenthe valve portion is moved away from the valve seat, the reliefmechanism allows at least part of the refrigerant flowing in from theupstream side to flow downstream via a gap between the valve portion andthe valve seat, the refrigerant flow passages, and the second throughhole.
 10. The expansion device according to claim 5, wherein the elasticmember is interposed between the stopper and the valve element, theexpansion device comprising an adjusting mechanism that adjusts aposition of the stopper within the cylinder, and wherein an elasticforce of the elastic member can be adjusted by adjusting the position ofthe stopper using the adjusting mechanism.
 11. The expansion deviceaccording to claim. 3, wherein the cylinder comprises: a valve seatportion in the form of a hollow cylinder that is fixed to an inside ofthe cylinder as a separate member, with one end thereof opening in anupstream direction, and an opposite end thereof being formed with thevalve seat, the valve seat portion communicating with the refrigerantpassage when the valve element is seated thereon; a large pipe portionthat has a passage cross-section larger than a passage cross-section ofthe valve seat portion, and has the valve portion inserted therein; anda guide pipe portion that has the guided portion inserted therein suchthat the guided portion is slidably supported therein, and has aflow-restricting portion formed at a downstream end thereof, theflow-restricting portion functioning as the restriction mechanism, andwherein the pressure-cancelling structure is formed by making thepassage cross-section of the valve seat portion larger than a passagecross-section of the guide pipe portion.
 12. The expansion deviceaccording to claim 11, wherein the guide pipe portion and the large pipeportion are configured to define a refrigerant flow passage that allowspassage of the refrigerant, between the guide pipe portion and the largepipe portion, and the piping of the refrigeration cycle, and wherein thelarge pipe portion has a side wall formed with at least onecommunication hole for causing an inside thereof to communicate with therefrigerant flow passage, and wherein the relief mechanism allows atleast part of the refrigerant flowing in from the upstream side to flowdownstream via a gap between the valve portion and the valve seat, thecommunication hole, and the refrigerant flow passage.
 13. The expansiondevice according to claim 11, comprising an adjusting mechanism thatadjusts a position of the valve seat portion within the cylinder, andwherein an elastic force of the elastic member can be adjusted via thevalve element by adjusting the position of the valve seat portion usingthe adjusting mechanism.
 14. The expansion device according to claim 3,wherein the cylinder has an introducing hole formed through a side wallthereof, for allowing the refrigerant to be introduced therein, andincludes a small pipe portion that slidably supports the guided portion,and a large pipe portion that has a passage cross-section larger than apassage cross-section of the small pipe portion, and has the valveportion inserted therein, and wherein at a pipe portion of the valveelement between the guided portion and the valve portion, a spaceportion is formed between the valve element and the small pipe portion,for communicating with the introducing hole, and wherein the pipeportion has an orifice hole formed through a side wall thereof, theorifice hole communicating between the space portion and the refrigerantpassage, and functioning as the restriction mechanism, and wherein whenthe valve element is seated, the refrigerant flowing in via the pipingof the refrigeration cycle is introduced into the refrigerant passagevia the introducing hole and the orifice hole, and wherein thepressure-canceling structure is formed by forming an expanded pipeportion in the small pipe portion, at a location in the vicinity of thevalve seat.
 15. The expansion device according to claim 14, wherein therelief mechanism is operable when the valve portion is moved away fromthe valve seat, to allow at least part of the refrigerant flowing infrom the upstream side to flow downstream via the space portion, and agap between the valve portion and the valve seat.
 16. The expansiondevice: according to claim 14, comprising: a stopper in the form of ahollow cylinder that is fixed to the cylinder, the elastic member beinginterposed between the stopper and the valve element; an adjustingmechanism that adjusts a position of the stopper within the cylinder,and wherein an elastic force of the elastic member can be adjusted byadjusting the position of the stopper using the adjusting mechanism. 17.The expansion device according to claim 2, wherein the cylindercomprises a small pipe portion that communicates with the refrigerantpassage when the valve element is seated on the valve seat, and a largepipe portion that has a passage cross-section larger than a passagecross-section of the small pipe portion, and has the valve elementinserted therein, the small pipe portion and the large pipe portionforming the stepped portion, and wherein, an upstream end of the valveelement is configured such that the upstream end is fitted into thesmall pipe portion by a predetermined amount when the valve element isseated, and the upstream end has a side wall formed with at least oneslit opening toward the small pipe portion, and wherein the reliefmechanism is configured such that when the valve portion is moved awayfrom the valve seat, the slit progressively increases an opening thatcommunicates between the small pipe portion and the large pipe portion,and when the upstream end of the valve element is removed from the smallpipe portion, the opening is rapidly increased, thereby allowing atleast part of the refrigerant flowing in from the upstream side tostepwise escape into the flow passage other than the refrigerant passageextending through the cylinder to thereby allow the refrigerant to flowdownstream.
 18. The expansion device according to claim 17, comprising:a stopper in the form of a hollow cylinder that is fixed to thecylinders, the elastic member being interposed between the stopper andthe valve element; an adjusting mechanism that adjusts a position of thestopper within the cylinder, and wherein an elastic force of the elasticmember can be adjusted by adjusting the position of the stopper usingthe adjusting mechanism.
 19. The expansion device according to claim 2,wherein the valve element having the pressure-cancelling structure, theelastic member urging the valve element, and the relief mechanism areprovided in a plurality of stages, from the upstream side to adownstream side within the cylinder, and wherein the relief mechanismsare configured to stepwise operate by adjusting respective elasticforces of the elastic members urging the valve elements.
 20. Anexpansion device that is disposed in a flow passage of refrigerantcirculating through a refrigeration cycle, comprising: a cylinder in theform of a hollow cylinder, the cylinder having a first valve seat formedby a stepped portion provided inside the hollow cylinder; a first valveelement that has a body in the form of a hollow cylinder inserted in thecylinder, and includes a valve portion that forms part of the body andcan be removably seated on the first valve seat, a guided portion thatis guided along an inner peripheral surface of the cylinder when thebody is moved to and away from the first valve seat, and a firstrefrigerant passage that extends through an inside of the body and has astepped portion formed therein at which the first refrigerant passage isexpanded in an upstream-to-downstream direction, the first refrigerantpassage allowing passage of the refrigerant; a first elastic member thatis disposed within the, cylinder, for urging the first valve element ina valve-closing direction; a pressure-cancelling structure that cancelsat least part of pressure of the refrigerant acting on the first valveelement in a valve-opening direction, the pressure-cancelling structure,comprising a valve-closing pressure-receiving surface that receivespressure of the refrigerant acting on the first valve element in thevalve-closing direction and has a pressure-receiving area smaller than apressure-receiving area of a valve-opening pressure-receiving surfacethat receives pressure of the refrigerant acting on the first valveelement in the valve-opening direction; a first relief mechanism that isoperable when a differential, pressure across the expansion device hasbecome equal to or higher than a first predetermined value to cause thevalve portion to be moved away from the first valve seat, to allow atleast part of the refrigerant flowing in from an upstream side to escapeinto a flow passage other than the first refrigerant passage within thecylinder to thereby allow the refrigerant to flow downstream; an innershaft member in the form of a hollow cylinder that is formed thereinwith a flow-restricting portion having a cross-section smaller than across-section of the first refrigerant passage, and is partiallyinserted into an expanded side of the stepped portion of the first valveelement, the inner shaft member protruding downstream from the firstvalve element; an inner cylinder in the form of a hollow cylinder thatis fixed to an inside of the cylinder, and has at least one slit formedthrough a side wall of an upstream end thereof, the upstream end beingcapable of having a downstream end of the inner shaft member engagedthereat, the inner cylinder being formed with a communication holeextending therethrough for communication with the flow-restrictingportion; a second valve element that has a body in the form of a hollowcylinder inserted in the inner cylinder, the second valve elementincluding a valve portion that forms part of the body of the secondvalve element and can be removably seated on a second valve seat formedon a downstream end face of the inner shaft member, a guided portionthat is guided along the communication hole when the body of the secondvalve element is moved to and away from the second valve seat, and asecond refrigerant passage that extends through an inside of the body ofthe second valve element and has a cross-section smaller than thecross-section of the flow-restricting portion; a second elastic memberthat is disposed within the inner cylinder, for urging the second valveelement in a valve-closing direction; and a second relief mechanism thatis operable when the differential pressure across the expansion devicehas become equal to or higher than a second predetermined value smallerthan the first predetermined value to cause the valve portion of thesecond valve element to be moved away from the second valve seat, toallow at least part of the refrigerant flowing in from the upstream sideto escape into a flow passage other than the second refrigerant passagewithin the inner cylinder to thereby allow the refrigerant to flowdownstream.
 21. The expansion device according to claim 20, wherein anamount of refrigerant allowed to escape by the first relief mechanism islarger than an amount of refrigerant allowed to escape by the secondrelief mechanism.
 22. The expansion device according to claim 20,wherein the first elastic member is interposed between the innercylinder and the first valve element, the expansion device comprising anadjusting mechanism that adjusts a position of the inner cylinder withinthe cylinder, and wherein an elastic force of the first elastic membercan be adjusted by adjusting the position of the inner cylinder usingthe adjusting mechanism.
 23. The expansion device according to claim 20,comprising: a stopper in the form of a hollow cylinder that is fixed tothe inner cylinder, the second elastic member being interposed betweenthe stopper and the second valve element; and a second adjustingmechanism that adjusts a position of the stopper within the innercylinder, and wherein an elastic force of the second elastic member canbe adjusted by adjusting a position of the stopper using the secondadjusting mechanism.
 24. The expansion device according to claim 5,wherein the valve element having the pressure-cancelling structure, theelastic member urging the valve element, the relief mechanism, the innershaft member, and the stopper are provided in two stages, from theupstream side to a downstream side within the cylinder, and wherein avalve seat is formed on a downstream end face of the stopper interposedbetween the two valve elements, for allowing a valve portion of thevalve element on a downstream side to be seated thereon, wherein theelastic members are interposed between the stoppers and the valveelements, respectively, the expansion device comprising adjustingmechanisms that adjust respective positions of the stoppers within thecylinder, and wherein elastic forces of the elastic members can beadjusted by adjusting the positions of the stoppers using the adjustingmechanisms, respectively.
 25. The expansion device according to claim 2,wherein, the cylinder includes a small pipe portion that communicateswith the refrigerant passage when the valve element is seated on thevalve seat, and a large pipe portion that has a passage cross-sectionlarger than a passage cross-section of the small pipe portion, and hasthe valve element inserted therein, the stepped portion being formed bythe small pipe portion and the large, pipe portion, and wherein when thevalve element is seated, an upstream end of the valve element isinserted into the small pipe portion with a predetermined spacing froman inner wall of the small pipe potion, and wherein when the valveportion is moved away from the valve seat, until the upstream end of thevalve element is removed from the small pipe portion, the reliefmechanism allows part of the refrigerant flowing in from the upstreamside to leak via the gap, and when the upstream end of the valve elementhas been removed from the small pipe portion, the relief mechanismallows the refrigerant to escape at a larger flow rate, whereby therefrigerant is allowed to stepwise escape into the flow passage otherthan the refrigerant passage through the cylinder to thereby allow therefrigerant to flow downstream.
 26. The expansion device according toclaim 25, comprising: a stopper in the form of a hollow cylinder that isfixed to the cylinder, the elastic member being interposed between thestopper and the valve element; an adjusting mechanism that adjusts aposition of the stopper within the cylinder, and wherein an elasticforce of the elastic member can be adjusted by adjusting the position ofthe stopper using the adjusting mechanism.
 27. The expansion deviceaccording to claim 2, wherein the valve element has a side wall formedwith at least one communication hole for communicating between an insideand an outside of the refrigerant passage, and wherein the reliefmechanisms includes a flow passage-switching structure that switchesbetween flow passages of the refrigerant by opening or closing thecommunication hole according to movement of the valve element.
 28. Theexpansion device according to claim 27, wherein the cylinder includes asmall pipe portion that communicates with the refrigerant passage whenthe valve element is seated on the valve seat, and a large pipe portionthat has a passage cross-section larger than a passage cross-section ofthe small pipe portion, and has the valve element inserted therein, thestepped portion being formed by the small pipe portion and the largepipe portion, and wherein an upstream end of the valve element isinserted inside an inner wall of the small pipe portion by apredetermined amount when the valve element is seated, and wherein therelief mechanism opens the communication hole to allow the refrigerantto escape, when the valve element is seated, and the relief mechanismkeeps the communication hole closed until the upstream end is removedfrom the small pipe portion, when the valve portion is moved away fromthe valve seat, and wherein when the upstream end of the valve elementis moved away from the small pipe portion, at least part of therefrigerant flowing in from the upstream side is allowed to escape intothe flow passage other than the refrigerant passage through the cylinderto flow downstream.
 29. The expansion device according to claim 27,comprising: a stopper in the form of a hollow cylinder that is fixed tothe cylinder, the elastic member being interposed between the stopperand the valve element; an adjusting mechanism that adjusts a position ofthe stopper within the cylinder, and wherein an elastic force of theelastic member can be adjusted by adjusting the position of the stopperusing the adjusting mechanism.
 30. The expansion device according toclaim 5, wherein the valve element having the pressure-cancellingstructure, the elastic member urging the valve element, and the reliefmechanism, the inner shaft member, and the stopper are provided in aplurality of stages, from the upstream side to a downstream side withinthe cylinder, wherein on a downstream end face of one of the stoppersinterposed between the valve elements, there is formed a valve seat forallowing the valve portion of one of the valve elements on a downstreamside of the stopper to be seated thereon, wherein the elastic membersare interposed between the stoppers and the valve elements,respectively, the expansion device comprising adjusting mechanisms thatadjust positions of the stoppers within the cylinder, respectively, therelief mechanisms are configured to sequentially operates from thedownstream side, in a stepwise manner, by adjusting elastic forces ofthe elastic members by adjusting the positions of the stoppers, usingthe adjusting mechanisms, respectively, and wherein the valve element onthe downstream side has a side wall formed with at least onecommunication hole for communicating between an inside and an outside ofthe refrigerant passage, and wherein a flow passage-switching structureis provided which switches the flow passage of the refrigerant byopening or closing the communication hole according to the movement ofthe valve element formed with the communication hole.
 31. The expansiondevice according to claim 30, wherein the flow passage-switchingmechanism causes the communication hole to be once closed during aprocess of rise in the differential pressure across the expansiondevice.
 32. An expansion device that is disposed in a flow passage ofrefrigerant circulating through a refrigeration cycle, comprising: acylinder in the form of a hollow cylinder that has a valve seat formedtherein; a valve element that has a body in the form of a hollowcylinder that is movably inserted in the cylinder and can define arefrigerant passage for allowing passage of refrigerant through thecylinder, the body having a portion forming a valve portion that can bemoved to and away from the valve seat; a restriction mechanism thatdecompresses the refrigerant passing through the refrigerant passage; anelastic member that is disposed within the cylinder, for urging thevalve element in a valve-closing direction; a pressure-cancellingstructure that cancels part of pressure of the-refrigerant acting onthe-valve element in a valve-opening direction, the pressure-cancellingstructure comprising a valve-opening pressure-receiving surface thatreceives pressure of the refrigerant acting on the valve element in thevalve-opening direction, and a valve-closing pressure-receiving surfacethat receives pressure of the refrigerant acting on the valve element inthe valve-closing direction; and a relief mechanism that is operablewhen the differential pressure across the expansion device has becomeequal to or higher than a predetermined value to cause the valve portionto be moved away from the valve seat, to open a flow passage other thanthe refrigerant passage extending through the cylinder by way of therestriction mechanism, to thereby allow at least part of the refrigerantflowing in from the upstream side to escape into the flow passage otherthan the refrigerant passage to flow downstream.
 33. The expansiondevice according to claim 32, wherein the valve seat is formed by astepped portion formed inside the cylinder, and the valve-openingpressure-receiving surface and the valve-closing pressure-receivingsurface of the valve element are both formed on an upstream side of therestriction mechanism, and wherein the restriction mechanism is formedby a gap between a reduced pipe portion provided downstream of the bodyof the valve element, and a shaft-like member partially inserted intothe reduced pipe portion.
 34. The expansion device according to claim33, wherein the valve-opening pressure-receiving surface is formed alsoby an upstream end face of the reduced pipe portion, and across-sectional shape of the reduced pipe portion is configured suchthat a pressure-receiving area of an entirety of the valve-openingpressure-receiving surface becomes larger than a pressure-receiving areaof an entirety of the valve-closing pressure-receiving surface.
 35. Theexpansion device according to claim 33, wherein the restrictionmechanism comprises a restriction flow passage formed by a gap betweenan inner peripheral end edge of the reduced pipe portion and an outerperipheral surface of the shaft-like member, and wherein a passagecross-section of the restriction flow passage is changed in anincreasing direction, when the valve element operates in a valve-openingdirection.
 36. The expansion device: according to claim 35, wherein anupstream end of the shaft-like member is formed with a tapered portion across-section of which increases upstream, and the restriction flowpassage is formed between a tapered surface of the tapered portion andan inner peripheral end edge of the reduced pipe portion.
 37. Theexpansion device according to claim 36, comprising an engaging memberthat is supported within the cylinder, and has the shaft-like memberengaged at a downstream end thereof; and an adjusting mechanism thatadjusts a position of the engaging member within the cylinder, andwherein a passage cross-section of the restriction passage in a closedstate of the valve element can be adjusted by adjusting a position ofthe shaft-like member by moving forward or backward the engaging memberusing the adjusting mechanism.
 38. The expansion device according toclaim 32, wherein the cylinder has a small pipe portion, and a largepipe portion, formed therein in an upstream-to-downstream order, byexpanding an inside thereof toward the downstream side, and wherein thevalve seat is supported within the large pipe portion, and wherein thevalve element is formed with the valve portion in the form of a hollowcylinder at a location downstream of the body, and has a reduced pipeportion extended upstream of the body such that the reduced pipe portionis movably inserted into the small pipe portion, and wherein therestriction mechanism is formed by a gap between the reduced pipeportion of the valve element and the small pipe portion of the cylinder.39. The expansion device according to claim 38, wherein thevalve-closing pressure-receiving surface is formed by an upstream endface of the reduced pipe portion, and the valve-closingpressure-receiving surface having a pressure-receiving area larger thana pressure-receiving area of the valve-closing pressure-receivingsurface is formed by a downstream facing surface of a stepped portionformed inside the body by the reduced pipe portion.
 40. The expansiondevice according to claim 39, wherein a downstream facing surface havinga cross-section larger than a cross-section of the valve portion isformed on a downstream side of the valve portion of the valve element,in a manner continuous therewith.
 41. The expansion device according toclaim 32, wherein the cylinder has a small pipe portion, and a largepipe portion, formed therein in an upstream-to-downstream order, byexpanding an inside thereof in a upstream-to-downstream direction, andthe expansion device including a guide pipe in the form of a bottomedhollow cylinder formed such that the guide pipe extends downstream froma downstream opening portion of the small pipe, with a downstream endthereof closed, and a communication hole formed through a side wallthereof in the vicinity of the downstream end, for communicating betweenan inside and an outside of the guide pipe, the guide pipe having thevalve element slidably fitted thereon, and wherein the valve elementhas, on an upstream side thereof, a guided portion that is slidablealong an outer peripheral surface of the guide pipe, and has a forwardend face which can be engaged at a downstream facing surface of astepped portion provided at a boundary between the small pipe portionand the large pipe portion, and the valve element is formed with areduced pipe portion at a downstream end thereof, thereby defining aspace portion for communicating with the communication hole, between thereduced pipe portion and the guided portion, and wherein in the spaceportion, the valve-closing pressure-receiving surface is formed by adownstream facing surface of the guided portion, and the valve-openingpressure-receiving surface larger in pressure-receiving area than thevalve-closing pressure-receiving surface is formed by an upstream endface of the reduced pipe portion, and wherein when the valve element isclose to the valve seat, a gap between the reduced pipe portion of thevalve element and the guide pipe forms a restriction passage as therestriction mechanism, and wherein the relief mechanism expands anopening area of the gap between the reduced pipe portion and the guidepipe against an urging force of the elastic member, to thereby allow therefrigerant flowing in from the upstream side to escape downstream at alarger flow rate.
 42. The expansion device according to claim 41,wherein a downstream end of the guide pipe is formed with a taperedportion a cross-section of which decreases downstream, and therestriction flow passage is formed between a tapered surface of thetapered portion and an inner peripheral end edge of the reduced pipeportion.